Park your car on the U.S. side and just walk across.
You don't have to walk far past customs before you get to the souvenir shops. They're everywhere, they pretty much off the same stuff at pretty much the same prices.
My recommendation - do some price shopping first, then you'll get an idea what you can ask for when you haggle. Take your time!
This is a nice place that'd be easy to miss as you drive through town. Good service, and (I thought) very good food.
Favorite Dish: The chicken mole was some of the best I've had, but they also had several other good dishes as well. Great lunch and breakfast buffets - all you can eat for $10.
Need a break from tacos and tortas? Hidden amongst the TD's and flop-houses near the border is a somewhat pricey alternative, that'll have you feeling like your'e back home again.
Favorite Dish: Chef's special shrimp and tenderloin brochette