Llanwrtyd Wells there's the Spa, Belle Vue Hotel, Neuadd Arms, Stone Croft. Or, if they're all shut and/or you're boracic there's a water tap on the west side of the garage
In Bont the shop shuts at something helpful like 2pm on a Saturday.
If you're bound northwards along a certain 200 mile route, the garage at Ponterwyd stays open until 10pm.