Steam deck case - I have been using spigen cases for anything I can for about a decade. This case also fits in the official case - https://a.co/d/cpbw5K7

Playvital back grips and thumb stick caps - Tbh I don’t use the back buttons on too many games, but these have been a game changer for comfort. Additionally, the thumb grip caps were probably the best investment. I got them just because, but they’re so worth it - https://a.co/d/2Kaz5Lb and https://a.co/d/h4yJ8Jf

Syncthings blew me away after I got it set up. Definitely recommend it

There are a lot of good suggestions here already. I want throw out Escape Academy. Split screen escape room game. My brother and I started playing it and had a blast in just an hour. Not sure about any story because we glossed over it, but we enjoy puzzles a lot.

Edit to include: Cuphead Wildermyth Overcooked 2 Terraria TMNT Shredders Revenge

I think if you’re not planning to play outside, go with one of the cheaper models and use the money saved to get an anti glare screen protector and SD card

The more cats the better.