Your beloved and widowed aunt recently purchased a car off of Craigslist on the cheap, but it's out of state. You're driving her there and following her back. It'll take about four days because she's not a power driver like you. Make sure you know everything you should know about this imaginary car in case you're asked... as well as where you're getting it (private seller would be the best for your tale).
If you use the dead relative, do it sort of begrudgingly... like, "I didn't really know my great uncle, but he and my dad were close so I gotta do it." Do that so you don't have to pretend to be mourning.