Stock up on favorite vegs, esp fragrant herbs. The most important thing is to get him started on food after he comes home. If he won’t eat, you’ll have to syringe feed him Critical Care or pellet mush (pellets soaked in water), so a feeding syringe is a good thing to have. The absolute majority of young boys won’t need syringe feeding though.
Something to keep him warm post op is also good. Hand warmers or a hot water bottle, wrapped in a fleece blanket. Buns can get cold after GA. He must have enough space so he can move away from the heat source if he doesn’t want it.
Serve water in a bowl, he might not want to work a bottle.
Keep him confined to his cage for 1-2 days, day 2 he can have playtime outside the cage, but no jumping or climbing.
Be prepared for a period of “post-neuter craze” – it doesn’t happen to all buns, but it does to some and it’s perfectly normal. It’s when the bun go on a hormonal roller coaster ride for 1-2 weeks or sometimes longer after having been de-sexed. Hormonally driven behavior can get very much enhanced during this time. That involves poop- and pee-marking, territoriality, cage aggression, mating behavior etc.