If somebody is waiting for my spot while I check my texts and make my calls before I drive, and starts getting antsy, ie: throwing their hands up in their car, or even worse, honking, I will absolutely, definitely have forgotten something in the store.
Actually, I often bring my stuff out from Costco, catch up on some phone calls and then get out and walk over to Michaels and Target, also both in the same shopping center. That is, if I don't have any frozen stuff.