Are you going to bring everything you have listed as well? This seems odd, I have done it once or twice when I did auctions. For instance something ended on Sunday and I traveled to SF on Monday and they hadn't paid, what I did was pack it up and weigh it if necessary, then bring the box and wait for them to pay. Once they pay I buy the postage, create the label as PDF and print it in the hotel business center, then tape it on the package and have the hotel mail it. Carrying packing supplies and a printer is a little cray cray yo, unless of course all of your traveling is by personal automobile then... Nope still wouldn't do it.
Marginally related: when I traveled for work it was a 13-state area around the midwest and most of the time I drove - company car (van, actually). The job was mostly driving - like - drive 3 hours, get to the town, check into hotel, then work for like 30 minutes, maybe an hour. The rest of the time I hit thrifts, resale shops and auctions (before I knew about clothing), and record shops. This was in the 90's, when you could still find tonnage of MCM in the thrifts and collectible vinyl for cheap. More times than I can count, I completely filled the van full of furniture and whatnots, and if I needed room I'd stop by antique shops and sell stuff along the way but keep any really nice stuff for when I got back to Chicago and could get top dollar. So anyway - yeah - selling as you go can be done though back then I only did it in person, not thru the mail.