Behold! This is something I've been passively working on for awhile (casually observing, lazily noticing?). I'm a fast foodie, I eat out A LOT and about a month ago I started observing the condiment packets in various restaurants and seeing what would be good for trail use and what I wouldn't use if I took it with me. There are so many places with such a greater variety than salt, pepper and ketchup that I decided to compile a list for the benefit of everyone (even if you don't eat fast food, you can still go in there and snag some free goodness). All of these things come in those little ~3g packets.
I'm skipping stuff like ketchup, mustard, salt and pepper because most places have those.
Chik Fil a- where I started this mighty endeavor, I've found that stores' contents vary slightly
-Frank's Red Hot sauce
-Purell Alcohol Towelettes (not food, but good to have)
If you go up to the counter and ask for a couple they won't even notice. (Come in 1oz packets)
-Chik fil a Sauce
-Presumptuous 'tude (compliments of me or other employees)
-Crushed Red Pepper
-Mild, Hot and Fire Sauce
-Green and Fire Roasted Salsa
-Zax Sauce (Sadly their hot sauces don't come in small sealed containers)
Gas stations are where the jackpots are
QuikTrip /Racetrack (god help you if you don't have one of these places near you, but any large hot dog selling gas station should have similar options)
-Salsa Del Sol
This is all I have so far, these are my main food places, if you have some other condiment caches you know of, add to my list!!