Personally, I like to divide my load between rear and low-rider front panniers. All four panniers can be small if not much gear is being carried.

For a multi-day tour, I'd recommend a small stove and fuel cannister. I got one from Canadian Tire here in Ontario Canada and the stove can almost fit into a jersey pocket. It's fantastic and welcome addition for those times when I want a hot drink to ward of a chilly morning or evening. Even a small fuel canister doesn't take up much room.

Cheers