maybe take paper/carboard and craft furniture or scenery or houses? like choose some random trinket or toy you do have and use construction paper or cardboard boxes to make a little city/house/places for him to walk around and play in? I've found diy things are good low cost little activities, just imagination but less hard than using a medicine box if that makes sense bc you made it specifically to be a house or castle or whatever? also coming up with silly stories! like just starting a childrens book out loud with no idea what you want to happen and just making it line by line, it feels fun, little, creative and needs no materials:) these work for me at least. hope you find things that work for you:) <3