I would say don't choose a bunch of stuff that would be overwhelming to deliver. Consider things that are already a part of your process, such as sketches, WIPS, thumbnails, tests, speedpaints, etc. You can show people how you do things, techniques, methods, etc. Early releases might also be easy if you create consistently and are able to continually deliver!
If you want to offer something even more substantial, maybe sketch requests to higher tier folks. I have a friend who will do monthly stickers or buttons to ship out to patrons. Just remember not to make it more work than you can handle! I always say underpromise and overdeliver!