I try to make a point to get something while I'm there, whatever I'm playing. I mostly go to Warhammer nights but there's a DnD/board game pub nearby too, either way I always get some paint or snacks or something. I usually encourage other players to support the store too if they can, or offer to spot them. It's just good behavior.
I want these places to stay open and as a (very tiny) small business myself, I know they appreciate it. Definitely beats ordering on Amazon.