I also have a messenger bag from Sportsman's Guide for extra gear. I also have a Coleman brand water bota, and a fanny pack with small water bottles (2 of them) for long treks. I can go a long time without food, but not H2O! (The kidneys were damaged by heart failure many years ago!)

As for sporran substitutes, I prefer my old leather fanny pack which affords ample room for all sorts of gear for an outing.

On the other hand, I would never go out without a proper sporran unless it was for a strenuous hike or some such. The above items are for very special events only.