Rawhide and dentabones works GREAT!

For chews, my rats get: dentabones (I reeeeally reccomend them, they are great!), petcetera rawhide chips (thin and round like potato chips, you can only buy them in Canada) Fortum honey flavoured rawhide hearts (thick heart shaped rings, they are made by Fortum, you can string these up from the roof of the cage, great fun!), compressed rawhide balls (balls made of rawhide, they are harder to get a hold of because they roll, they provide a challenge) pigs ears, wood, and that's all that they have in their cage at the moment

For the water bottle, try pushing Toshi up to it and poke his nose on the ball a few times so his nose gets wet He'll learn quickly

For treats, I usually give them some food that is part of their dinner food, so then I can give it to them then instead of for dinner. But actual treat treats that they rarely get, are most fruits (I try to avoid sugar, so I only give them their homemade frozen fruit meals three times a week), chocolate ( I also give it to them if they sound like they are coming down with something) and a few other things that probably aren't the best lol

To keep him busy, you could try teaching him tricks My rats know some