Sometimes, for canning, after a hard day in a hot kitchen (or not so hot), sometimes I'm just "done" and I get something out for dinner. I rarely eat out, so it's kind of nice.
When I had a big overtime-heavy job at work (14 12 hour nights in a row), after an overtime heavy year (I had over 400 hours of overtime that year), I rewarded myself with a DSLR camera.
Rewards are usually small though, a good piece of chocolate, a rich dessert, etc.