A portable kayak. I really want to get into kayaking more seriously, but I'm pretty hampered by where I live (SoCal, no inland kayaking within an hour's drive). There is some kayaking in bays/inlets, though it's 20-40 minutes of driving, then fighting for parking, and lugging a kayak several hundred feet. I also don't have the room for a rigid kayak at home.
However, I've been toying with the idea of a decent inflatable that I could attach to my e-bike trailer. I think I'm trying to balance aspirations and reality; it sounds great to bike to the beach, hop on a kayak, and bike back. However, it might be enough extra effort that I wouldn't do it often enough to justify - riding to the beach (7 miles each way), inflating the kayak, paddling around, deflating, drying and repacking the kayak, and riding back isn't a quick trip. That would be several hours, and I don't often get those blocks of time.
Nevertheless, it's fun to fantasize a bit. Currently favoring the Advanced Elements Expedition Elite.