I saw someone say cup holder I 2nd tht. b I got one of these style cup holders at a garage sale best dollar I ever spent these these self leveling ones are great they prevent you from spilling hot coffee on yourself wasent this exact one... it's a mater of one that will work for there chair...
I use this for a drink holder https://www.amazon.com/gp/product/B00PAQKQH6/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1 It's not perfect, but it works pretty good. As for the coolers, I use a couple of lunch bags I got from target for less than 10 bucks each. They seem to be the exact same size as the Zuca coolers, but cost much less.
Just get one that's on gimbals
The only things that I could think of that might help is this self-leveling cup holder, you can DIY attach it to the desk on the right side (in a way that it levels itself out whenever you incline the desk) and use a cup to hold whatever stationery you want,,
If you want the pencils to stay on the desk itself, you could buy these adhesive pencil clips to stick to the desk and just have your pencils/paintbrushes on there as well (just make sure the clips fit the pencils)
i also suggest adding a picture of the desk to your post, so people can see what they're dealing with here 😅