I always travel two-up and my saddlebags stay packed 12 months out of the year.
On one side, Got a gallon of gas, siphon hose (used to travel with a person on a V-Rod), my rain suit, rain over gloves, spare fleece vest, travel bike cover, tire plug kit with the CO2 carteridges. The other side, my wifes rain suit, spare fleece vest, H-D tool kit, another tool kit about that size with a few good wrenches, pliers, fuses, 3' of wire, 27 Torx screwdriver, etc., a First-Aid Kit I bought from Aerostitch, another First-Aid kit I put together about the same size (lots of 4 x 4 pads, tape, scissors, benadryl, usual stuff), 1 qt of oil. The tour-pak will have some light sticks, tape and few more goodies.
The clothes for a trip we can get in the bag mounted on the tour-pak, after all you only need the clothes you got on and one other pair of jeans, a few t-shirts (you will buy more), socks and underwear.
Like somebody else stated before, you can always buy stuff along the way.