I want to go fishing for red drum (reds) on the Texas Gulf Coast and I would like to use live bait. What types of live bait should I use?
Depending on the time of the year, the water temperature, the mood of the fish, and the available food for them, fish (esp. salt water) will feed on any number of different bait fish. Rather than recommend a specific bait fish, as this can change depending on the above conditions here is what I suggest.
Go to a local tackle shop and ask. Tackle shops are cornucopias of information, especially for localized fishing like you are describing. They will likely already have live bait fish such as keelies, minnows, or shiners for sale for you to try out and if not they should definitely have bloodworms and squid strips, which brings me to...
Use live bait, like worms/squid/shrimp, to catch bait fish to use for the drum. Even though it is listed as 2) here, this is by far my recommended method. There is nothing better than finding a school of bait fish in the same spot of ocean that you are fishing for drum in. The bait fish are fresh and more importantly they are already what the drum is used to eating. For this, I suggest a high-low rig that sits on the bottom, keep the line taught, and use small hooks with a small piece of worm/squid/shrimp on each. Alternatively, if you find that a school of bait fish is at the surface and they are big enough (larger than 6 inches) you can snag them with a weighted treble hook. Basically, cast the weighted treble past the school of bait and then reel, reel, reel as fast as possible and rip the hook through the school. This should foul hook the bait which you can then immediately cut up or use as live bait.
If neither of these previous two options are possible, I would suggest trying artificial baits. I know that was not your question but it is hard for many salt water fish to resist a nice fat Gulp on a brightly colored bucktail. Jigging works best with this presentation.