I'd certainly not want to play anything to impress anyone in the shop but 'Celebrate' by The Fields of the Nephilim (it's a picky chordal bassline) and 'Calm Down, Come Down' by Throwing Muses would be two as I know what they sound and feel like on my own basses,and then maybe something I'd learned recently as it would be fresh in my mind.
Other than that, some scales and chromatic runs to get a feel for how the bass plays
Mind you, I'd be in there on a wet Tuesday afternoon to minimise the number of spectators !