We eat out often after shopping. If I could carry the pen in my purse, I'd take it on a more regualr basis.
Your pharmacist is correct, but you shouldn't let the pen get superhot. Don't set it on the windowsill in the sunshine, don't leave it in your car in the summer. If you don't have air conditioning at home, it would be prudent to keep it in the fridge on hot summer days.
A few minutes in heat as you go from your home to a restaurant shouldn't cause problems. To be extra safe, especially if you're going to be at a picnic on a hot summer day, you could get one of those Frio pouches that keep insulin cool.
Here's a release about this.