I've done it a number of times, not on purpose just worked out. It was always during a festival at Epcot so my lunch and sometimes my supper came from booths. I got up early and didn't have anything to do so rode the bus to AK for rope drop. Got breakfast at the little stand near Safari. Rode Safari and EE, walked both trails and left. (no FPs) went to HS rode ToT and GMR (oh how I miss it) walked around and shopped and walked to Epcot (no FPs) grab a few snacks while walking through Epcot and got on the monorail to MK. While on the monorail grabbed a FP for BTMRR and Pirates, rode people move and CoP and back to the monorail and back to Epcot. Rode SSE and walked over to the Land and rode that. Walked back through Epcot snacking at booths along the way. I think AK had extra morning hours that day and since it was Sept. all parks were open late. I've done it a couple of times, just moving from park to park on a whim with nothing in mind, standing in the shorter lines and just snacking along the way. It's not uncommon at all for us to hop to at least 3 parks in a day and when I'm solo 4 parks is not uncommon, I don't always ride anything at some of the parks, I've been known to hop over to MK just to shop on main street and leave or hop to HS to grab lunch at HBD Lounge and leave.