Depends on your mileage and touring approach.
Just done a 2day fix-wheel tour Edinburgh to Donegal - a 200mile then a 150mile day. If it's a high mileage light tour you should be packing as light as possible.
If you're not needing to stay somewhere i.e leaving your tent set up with your gear in it as you go off to do other things I suggest a bivvi-bag is a better bet. Lighter and if you leave your mat and sleeping bag inside you can just roll it up as a single bedding roll. Easy and you can transition from being on the road to being asleep within 5 minutes and back again!
Beyond that a small always-open bag which is easily accessible for food to go in as you ride. You shouldn't have to stop to unclip bags to eat and you should be eating small amounts near constantly - a variety of different textures of food so you don't get bored.
If it's a long multi-day audax-style tour - try aero-bars. REALLY! high and rearward to add another position, more aerodynamic whilst supporting your upper-boy. a la RAAM and Tour-divide riders.