These are my suggestions, things I do on my trips.
1. Park on US side at the motel parking ($4 wkdays/$9 wkends for 8hrs.) next to Jack in the Box, near the end of Trolly track. This saves you the long walk across the bridge when coming back, since it is close to the customs exit. After a long night of drinking/f***ing/whatever you'll be doing in TJ, it's nice to have a short walk back to the car.
2. Definitely bring a passport/visa. I've been there recently and saw people get hassled for not having the proper re-entry doc. They were not let through, but were sent to a second desk. Not sure what happens there, but could be a major inconvenience/delay.
3. I bring just what I need, enough money for activities, passport, and driver's license, all kept in front pockets, just in case.
4. After parking, walk across the pedestrian bridge, cross, and take taxi ($5) to Adelita's, as mentioned by others.
5. Hit Adelitas, Chicago, and Hong Kong or others within the area. Avoid walking in dark or not well lit areas where there's not much people around, as this will make you vulnerable to TJ cops, who are notorious for stopping people and extorting money, or other unwanted characters.
6. When taking a cab back to US border, make sure get dropped off at the Sentry and not the Yellow Taxi parking. This saves having to walk across the ped bridge on the Mexico side to get to customs.
Have fun, be safe, and enjoy TJ!!