I'm currently using a small Carradice saddlebag with a bagman Q/R. Room for a change of clothes and a few tools and spares. For the winter, I'll probably re-fit the rack and use a rack bag, which has a slightly bigger capacity, and then I have the option of using a pannier if I want to carry some extra clothing or do a bit of shopping. Rucksacks are just a pain for anything over 4 or 5 miles.