wow. Real Tex/Mex is a million miles from here. :p

My first thoughts went with brightly colored hot peppers, bottles of hot sauce, and small cactus plants -- the latter two would make good favors and somebody like me would be more than happy to take any extra hot peppers off your hands when the party is over. :)

I did some quick searches and the first thing that struck me was perhaps using a brightly colored sarape to cover or drape the tables... and what about using maracas as decor and favors?! I assume they're available in your location, but up here we'd have to go to a place like Party City to get them. lol! Here's a link to "fiesta" stuff at Party City:
fiesta party favors

***####!!!!
I just typed a long response and my computer burped and I lost the whole thing!!! AAARRRGGGHHH!!!

Piggybacking on PM's idea...use the hot sauce and make cute rehearsal dinner labels for the bottles.
eg: Some Like It Hot!
John and Mary
March 31, 2013

Buy etching cream and small votive cups. Make a stencil, and etch the couples information into the cups for guest favors.

Use Gerbera daisies in mason jars down the table centers. Real or silk, they come in bright colors.

Make your own napkins using a fun print or brightly colored solids. You could match the color of the daisies.
Think hot pink, orange, lime green, yellow, turquoise, red. If you don;t sew, cut them out with pinking shears.

Make napkin rings out of carboard tubes covered with fabric, or buy inexpensive ones, and cut out cactus shapes from felt or cardstock and glue to the napkin rings.

You might be able to find small pinatas at a party supply store with a wedding theme and use as centerpieces.

Colorful candles are always a good choice.

Use different colored package shreds and spread them in the middle as table scatter.

I'm going to try to post now before this goes away again, LOL

Candy