I often get asked (by those who know I prep), "How do I prep on a budget? I don't have land, what can I do?"
Here's the answer I give:
In this scenario, it's important to focus on the TOOLS and KNOWLEDGE that allow you to OBTAIN (vs. stockpile) the items you need. None of these items are expensive (except the handgun, of course, but see suggestion there), and even at minimum wage, you should be able to obtain these with no problem.
WATER - you NEED two things. 1) A metal water bottle you can boil water in. 2) A water filter straw for quick water on the go. Knowledge wise, know where to find water in your area (even if a city).
FOOD - 1) A small can opener (will keep you from injury when opening found cans), 2) A small camping mess kit (something to eat out of, cook in), 3) Leakproof bags (to carry food in). Knowledge wise, know local plants that are edible, where you can find fish, game, etc. (even if just squirrel or pigeon, etc.). Don't be picky, even bugs, etc. Seeds are great, but only if you find a safe place for them, and know how to get them going/producing.
KNIFE - both protection and as a tool, a good fixed blade knife is essential
MULTI-TOOL - really handy, so many uses.
LIGHTER - you need fire, and these work fast. Other firestarter methods are great, but this one is essential.
FLASHLIGHT - LED one, just good to have.
PONCHO - not one of the $1 ones (though those are good to have as well), but something that will really keep you dry, or can be used in a makeshift shelter.
RADIO, HANDCRANK - get one that also has a light, and cell phone charger outlet. You can keep a TON of pdfs on a smart phone, and use this to keep it charged enough to read the docs. This is great for the Knowledge portion here. Not to mention, a radio can let you know what SHTF crap is going down.
HANDGUN - of course, if you have one, or can get one, this is essential (as well as ammo). If you don't have one, this should be one of the first goals (to loot one), as without it, you may not be able to KEEP any of the above items. That said, I also warn against trying to OBTAIN from preppers. First off, they will shoot you dead (softer targets await, each move should be a risk assessment). Second, it's just bad form.
Lastly, if you KNOW a prepper, maybe have a conversation. Preppers need PEOPLE, and there are plenty of things a non-prepper can do to earn his/her keep with them.