Rats are too small , maybe those pig rats could have flint lol , but its not it , if we had seagulls that would be a another story, you could even find a lighter there and bottle caps.
As you can see , sadly they eat a lot of junk
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Any how main thing is monster drops something like meat , tail , skull or intestines.
For a simple example lets take floater , he could drop:
1. Ganglions 2. Ovipositors 3. fore mouths 4. Float sacs 5.Floater meat( you can use all of these as a quest item in various quests , including ones that could lead to Perks , Titles , Achievements in long chain quests.)
6.Floatation bladder(contains noxious gases) you could use these to make a special kind of fuel for flamethrower or bomb , or use it as a new type of fuel gas for cars(if you upgrade car to use gas). Or simple use it as an quest item.
And you could use all of these for cooking(if we consider it).
It could give possibilities for various kind of food that could heal you , regenerate you , give you some Stat bonuses , kill you , poison you , give you radiation ( i know that stuff that give you those bonuses already exist and there is no use to make new stuff , tho in wasteland not everyone had access to chem labs so they could make drugs , so they used everything they could to make stuff with different effect .) Those in Arroyo , they certainly knew some crazy shit to make