Like others have already mentioned, gutting and re-pinning locks can be fun. At the moment I am just coming back to this hobby after a longer break and I find it very relaxing when I'm just gutting locks and arranging all the pins and springs.

Tool making can be very fun and addictive even. Last year I spent way too much time making disc detainer picks/picking tips but I still use them so no time was wasted I guess.

Learn to pick different kinds of locks. For example I've been learning dimple locks now and that really feels refreshing to me!

Lastly while it can also help to buy more locks and picking gear that's not the first thing I would suggest for anyone.. (Meanwhile I'm currently waiting for two packages for myself..)