You are not allowed to accumulate assets that the US government can see (past $2,000, if I recall correctly), rendering it extremely difficult to plan for the future. (The shoebox under the bed is a plausible strategy for saving, but if it is discovered, you may get accused of drug dealing and/or tax evasion.)

It wouldn't only look like tax evasion but effectively be tax evasion.

You might do some online work that pays you in bitcoins.