Probably the longest driving trip I did was from MI (near Detroit) to Toronto for a conference for a few days, then about a week of vacation driving through Montreal (I was going to stop, but got worried when all the road signs turned into French only, so kept going), entered the US through ME, down along the East coast, into MA, CT, NY, then down to VA and finally returning via WV, PA and OH back to MI. I also zig-zagged up and down the coast a little. I was going to spend most of the week in VA, but when there were thunderstorms predicted the entire week, after I got to NY, I headed back up to MA again for a few more days, and then did the trip home with just a stop to see Luray Caverns and various scenic outlooks.
It's the only time I've ever traveled without having reservations anywhere (other than for the conference in Toronto). It was great fun, because I wasn't committed to any fixed schedule. If I got somewhere and wanted to spend an extra day by a pool at the hotel reading a book, I could. If I didn't get to see all the sights I wanted to see in a town in one day, I could just book an extra day. I just stayed in cheap motels along the way, and never ran into any problems finding places with vacancies along my route. If a place didn't have any vacancies, I just headed to the next exit or next town and found a place that did (I wasn't usually driving late into the night before looking for a hotel...I pretty much was stopping around dinner time each day, so wasn't pressed for time). The biggest advantage really was being able to just change my mind at the last minute, when I saw thunderstorms headed for the beach towns I was planning to visit.