I know I won't regret a penny I spend on art commissions. The 401k could be a toss up. As always the standard advice applies (and is easy to say and hard to do if you don't have enough money)
* diversify: have a pension, savings, keep track of your Social Security but also buy a house or apartment if you can.
* Avoid things like bitcoin and gold unless you are an expert in commodities.
* Always look at reoccurring expenses cumulatively over at least 5 years.
anything else?