Here are some basic guidelines that are pretty universal when it comes to urban Foraging (aka Dumpster Diving). You may already know them or have an idea about them and probably no two divers will have all the same guidelines so here are mine.
1. (Be safe)-Don’t dive alone unless you are absolutely sure it is safe to do so.
Having another person with you could save your life. Being inside a dumpster when a truck comes to dump it is not a good idea and having someone outside keeping watch for trucks, people who might not have your best interest at heart and just to hand stuff to will help a lot. The spotter needs to keep a look out at all times and needs to be ready to hand you bags or take stuff from you if need be. Having a spotter is important and very helpful in most situations.
Of course if you only have stops that are somewhat secluded and quiet so that you can hear a truck coming or can see someone walking in your direction long before they get to you then maybe diving alone is an option.
2. (Be safe)-Scope out your potential dive stops in the day time if possible. This lets you see things you wouldn’t normally see.
3. (Be safe)-Choose stops that are well lit and secluded first and only take the more dangerous stops if they are very productive and worth the risk and you have a spotter.
4. (Be safe)-You will be surprised at how much of the food you think may be spoiled is actually just fine.
With that in mind though, don’t take chances. If in doubt, throw it out.
Smell is the number one tell and your best defense against food poisoning. If it is bad it will not smell right. It helps to have another nose or two around to help confirm your thoughts on good or bad smell. Feel is also an indicator (ie. meat=slimy/mucousy=probably bad).
You can’t always go by sight but it certainly weighs in to the equation. Puffy packaging is not always an indication of bad/spoiled food but more times than not, it is.
You can do a lot (not all) of these test while you are diving. You see a puffy package, poke it and smell right at the hole while making the air inside come out. If you’re not sure, take it home and test it further. Bad, leave it.
5. (Be safe)-This one I am not so good on and is optional but I think it is a good practice to be in and I try to do.
Evaluate your take as soon as you get it home. Repackage and label everything that is good and throw out or give to your (or friends/neighbors) animals anything that is off or bad (with their permission of course).
Dogs, cats, pigs, hogs, etc. love the spoiled meat. Unless they are old or very young or very domesticated, you should be ok with giving it to them.
Repackaging it does a few of things. First, you get a chance to smell and feel it to determine if it is good or bad. Second you put it into a clean package so you reduce the chance of contamination from bad bacteria that might be present on the outsides of the packages you just retrieved from the dumpster. Then it also keeps your freezer, fridge or cabinet from being over crowded with food that you can’t use anyway (saves space).
4. (Be prepared)-If you are diving for food, take a cooler or cooler bag with an ice pack or frozen bottles to get your cold foods cool as soon as possible.
5. (Be prepared)-Take some lengths of paracord, duck tape, packing tape, bags (more than one kind is a good idea) and containers with lids to organize your take in (if you are in a vehicle).
6. (Make it fun)-Don’t be afraid to mix it up or change your route. If you are looking mostly for food, branch out broaden your search. You never know what you may find that will be exactly what you are looking for or needed (has happened many times for me).
7. (Keep it clean)-Pick up around the area. Make the owners glad you visited their dumpster.
They have to deal with people dumping their trash in their dumpster, low paid employees not caring about missing the trash can, etc. If you clean up and always clean up, they will notice and they may reward you on occasion with some good finds.
8. (Keep it clean)-Close up the dumpster before you leave. You don’t want to leave it open and the wind come along and blow trash out all over their area or animals dragging the trash out and making a mess, because you left it open. The owners won’t like that.
9. (Share)-If you can’t use it all or share it with someone, leave it. Don’t take more than you can use. It helps if you have farm animals or pets that you can share spoiled goods with or maybe a neighbor or friend that does.
10. (Keep your stops secret)-No matter how much you want to shout it to the world. No matter how proud you are of your finds. DO NOT share your specific sites with anyone, unless you trust them completely to respect your dive days/nights. Share your finds, share the bounty, but never share the site.
There are probably more but these are a few I could think of. I hope that they might be of some help or inspiration and of course you will certainly come up with your own way of doing things.
Good luck and happy foraging!