Consumables
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Consumables in KoL are computed thusly:
Each consumable has a minadv, and a maxadv. These two values are internal to the database. The player never sees these. Both minadv and maxadv are integers.
When a food or drink is consumed, the following happens:
 The game chooses a value between minadv and maxadv in a uniformly random fashion.
 munchies pills bonus adventures are computed and added.
 Ol' Scratch's salad fork and Frosty's frosty mug bonus adventures are computed and added.
 milk of magnesium and The Ode to Booze bonus adventures are added.
 tuxedo shirt gets added on for applicable drinks.
 Salty Mouth gets added on, for applicable drinks.
 Opossum and Blender bonus adventures are added, if applicable.
Size and Quality
Many consumables also have a Size (equal to the fullness/drunkenness of that item) and a Quality (value chosen to make adventure gains better). The S/Q paradigm denotes that a food uses Size and Quality to determine its minadv and maxadv. Most older (NS11) consumables follow S/Q. Size and Quality are very important for crafted consumables, when two craftable things are put together, the Size and Quality values of the two get added together.
For any consumables following S/Q:
 minadv=Size
 maxadv=Size*Quality
Range Chopping
For a Food, if the difference between minadv and maxadv is greater than 7, then a chop is performed from either end of the range. For a Booze, if the difference between minadv and maxadv is greater than 5, a chop is performed. This chop is equal to:
 Food: floor((maxadvminadv6)/2) from both sides.
 Booze: floor((maxadvminadv4)/2) from both sides.
Consequences
Because of this, a food that has been chopped will always have its unmodified observed range be 6 or 7, due to the following:
 T = top of range, B = bottom of range, M=max, m=min.
 T = M  floor((Mm6)/2)
 B = m + floor((Mm6)/2)
 T  B = M  floor((M  m  6)/2)  m  floor((M  m  6)/2)
 = M  m  2*floor((M  m) / 2) + 6
 Notice that if (M  m) is even, then it is exactly 6, and if (M  m) is odd, then it is exactly 7.
 = 6 + (0 or 1)
Similarly, a booze that has been chopped will always have its unmodified observed range be 4 or 5.
What to take away from this: If a food's unmodified observed range is not 6 or 7, then either it has not been chopped, or the food has been messed with in some way by the game designers. Similar logic can be applied for a booze which has a range that is not 4 or 5.
Furthermore, if a food's unmodified observed range is less than 6, and the minimum of the range is not equal to the Size, then the food is messed with. Similarly for a booze's unmodified observed range being less than 4.
Other Consumables
There are also many consumables which do not follow the S/Q pattern. Supernova Champagne is an example. Its range is hardcoded 711. While that would fit with S=3, Q=5, it does not fit, due to how Blender used to work (unverifiable ingame now). These types of consumables are assumed to have their minadv and maxadv hardcoded. Every consumable added to the game since NS13 is believed to be hardcoded.
Examples of Size and Quality
A Booze example
Size and Quality values are added together for craftable things. Basic booze has S=3 and Q=1, basic fruits have S=1 and Q=1, and cocktail garnishes have Q=3. Therefore, Advanced Cocktails are S=4 and Q=5. Their minadv is 4, and their maxadv is 20. They get chopped by floor(2044)/2 = 6 from both sides, producing the range 1014. So the minimum observable value without modifiers is 10, and the maximum is 14.
A Food example
Hi meins are S=5 and Q=8.9. Their minadv is 5, and their maxadv is 44, they get chopped by floor(4456)/2 = 16 from both sides, producing the range 2128. So the minimum is 21, and the maximum is 28.
Stated Consumable Quality
Consumables give a rough indication of how good they are in their item description. The stated quality is based solely on average adventures per size. This table shows the breakpoints.
Quality  Adv/Size 

EPIC  5.01+ 
awesome  3.015.00 
good  2.013.00 
decent  1.012.00 
crappy  01.00 
Modifiers
Munchies pills add adventures to Food in a tiered fashion. If the actual amount of adventures that the consumable would give you is in the following ranges, then Munchies pills will add a specific amount.
Raw Food Adventures 
Bonus Munchies Adventures 

13  +3 
46  +2 
7+  +1 
As an example: A boring spaghetti giving you 4 adventures would gain +2 adventures from a munchies pill, and a boring spaghetti giving you 10 adventures would give you +1 from a munchies pill. Alternatively, if you got 9 adventures from a boring spaghetti eaten with only a munchies pill, you would know that the base roll must have been 8 adventures.
Then Milk of magnesium and Ode to Booze are added on. These will add as many adventures as the size of the consumable. For example, a boring spaghetti will get +3 adventures from Milk, and a corpsedriver will get +6 adventures from Ode.
Frosty's frosty mug increases adventures gained from booze by 30%, rounded down. If the booze is a beer, however, adventures are increased by 50%, also rounded down.
Ol' Scratch's salad fork increases adventures gained from food by 30%, rounded up. If the food is a salad, however, adventures are increased by 50%, also rounded up.
After that, for applicable beers, Salty Mouth gives a 46 adventure boost uniformrandomly.
Finally, for applicable boozes, the Tuxedo shirt gives a 13 adventure boost uniformrandomly.
Example with Modifiers
This example will show how Superhuman Cocktails behave when modified by Ode and Frosty's Mug.
It may be easier to follow along with this example by looking at the table below, since sometimes it is not readily clear why the math works out the way it does.
Superhuman Cocktails are minadv 4, with maxadv 28. This means the chop is floor(2844)/2 = 10. This means that the base range is 1418. The average of this range is 16.0.
Applying Ode to this increases all values of this chopped range by 4, which makes the range 1822. The average of this range is 20.0.
Finally, drinking with Frosty's Mug increases all values of the range by 30%, but they are floored. This can be seen in the table below. Frosty's Mug acts after everything else, so 1822 are chosen to be modified.
The average must be calculated by finding the weighted average of each possible value that's produced from the range.
 floor(18 * 1.3) = 23, occurs with a 20% chance
 floor(19 * 1.3) = 24, occurs with a 20% chance
 floor(20 * 1.3) = 26, occurs with a 20% chance
 floor(21 * 1.3) = 27, occurs with a 20% chance
 floor(22 * 1.3) = 28, occurs with a 20% chance
The weighted average is the sum of each possible value multiplied by its probability of occurring. In this case, the range is 2338, and the average is 25.6. Frosty's mug affects the drink's observable values in a predictable way, and that's why there are jumps in the observable values between 24 and 26.
Modifiers  Possible Values  Average  

Chance  20%  20%  20%  20%  20%  
Base  14  15  16  17  18  16.00 
+Ode  18  19  20  21  22  20.00 
+Frosty  18  19  20  22  23  20.40 
+Ode and Frosty  23  24  26  27  28  25.60 
A Food Example
The math is the same idea for Food and Booze alike, here is an example of hi meins. Notice that, like with the Booze example above, there are jumps in the amount of adventures that are observable. So with a Fork, a player will never see an adventure gain of 31 or 35 for a hi mein.
Modifiers  Possible Values  Average  

Chance  12.5%  12.5%  12.5%  12.5%  12.5%  12.5%  12.5%  12.5%  
Base  21  22  23  24  25  26  27  28  24.50 
+Munchies  22  23  24  25  26  27  28  29  25.50 
+Milk  26  27  28  29  30  31  32  33  29.50 
+Fork  28  29  30  32  33  34  36  37  32.80 
+Munchies and Milk  27  28  29  30  31  32  33  34  30.50 
+Milk and Fork  34  36  37  38  39  41  42  43  38.75 
+Munchies, Milk, Fork  36  37  38  39  41  42  43  45  40.12 