Creatine is so cheap, it's hard to imagine doing without it.
Essential for me:
Protein powder (really like whey isolate during workout)
Creatine - cheap
Ground Flax meal (fiber, Omega 3) - cheap
Fish Oil (seems to help with mood and recovery)
Vitamin C - cheap
If everything went to hell financially, I would be okay with those supplements.
Truth is, you can make a lot of progress without any supplements, just with food.