On a long bus trip I usually take a soft sided, insulated bag with drinks and snacks. A heavy shawl, even in summer because the buses I took were always chilly inside. And a large purse/bag, but with my money and important papers (driver's lic, etc) in an inside pocket in my jacket or vest.
Any medicines necessary, pain killers, etc. Glass wipes. Tissues.
(I SAID large purse or bag, you'll need it.)
Some tour groups handed out large plastic bags with ties and felt tips to put names on them when time came to go home. The storage under the seats, accessed from outside, was where they put all our purchases. Names on them really did help when we were tired and wanting to go to our cars with the correct items we had bought.