I know only two one-word words:

• Unpretentious
• Modest

I think if seeking about food, clothes or likes in general then the first word is your best choice.

I know only two one-word words, but both are rather formal:

• Unpretentious
• Modest

You could also say "not too picky" or "not too demanding".

If about food, you could say "hearty eater".