Here are some ideas:
1. Full front triangle bag with holes for the cage mount bolts. If you want to carry 2 water bottles just put in 2 cages. One bottle only needs one cage. No bottles means full size frame bag. Plus you won't need Velcro on the down or seat tubes since you can attach the bag with the bottle cage bolts.
2. Elastic or Velcro in the bag underneath the top tube to hold items such as tent poles, stakes, tarps, etc.
3. I have a full length pocket inside just below the zipper for food and quick access small items.
4. I gave my frame bag a flat bottom about 3 inches long to make sure I didn't lose any small items in the pointy crevice at the bottom of the bag.
5. I also added a bit of Velcro to attach a tank bag with the frame bag.
6. I would like add a mount for a bladder but haven't figured it out yet.
Sent from my hammock