Most folks have a good idea about how to get to South Padre Island - coming from the north, you'd hook up the Highway 77 south of Corpus Christi and drive forever, hit Route 100 south of Harlingen and San Benito, and you're there. Coming from Austin, you could follow I-35 to San Antonio and then take #37 to Corpus Christi, although we always take the route from San Marcos to Seguin, Karnes City, Kennedy, Stockton, and then #37. Less traffic, more fun ... and importantly, some great pit-stops.
OK, you're not going to see panaoramic views of the Grand Canyon or the Shenendoah Mountains, but we like the back way. The drive from Austin to Padre is a little over 6 hours if you stay less than 4 miles over the speed limit. Chances are you're going to get thirsty and, if logic holds, you'll be needing a pit-stop after a couple bevvies - and if you're traveling with ladies, they will let you know, if not in English then with international distress signals.
The first rule of thumb is that all McDonalds and Dairy Queens are handy candidates. Watch out for the McDonalds in Robstown just south of Corpus Christi - it might turn you around towards McAllen if you're not careful. The first fast-pee joint we hit on the way down from Austin is the one in San Marcos. Not too bad, although the food has been an issue sometimes (which is why we pack snacks now).
We usually make it through Seguin although they have some fairly good BBQ there from what I've heard. Our next stop is a little Chevron convenience store in Karnes City. As far as convenience stores, this one is good, with clean facilities and some great fried chicken in case you have the munchies too. You could go further to Kennedy (the two towns are intense rivals) where they have a "sawsage farm," a roadhouse and a Walmart with a McDonalds in it.
There aren't many places from here south to Beeville, except for a Shamrock in Pettus. The facilities in Pettus get an "A" but the muchie bags we bought there have all been stale. Beeville used to be "Pee-Ville" to us until they closed the one on Charco road and another closer to town on the access road; the guys at the exit to the main drag were surly last time so I avoid it like the plague now.
I also avoid Skidmore, the next town to the south, unless you're desperate - in that case, check out the Dairy Queen and don't look the manager in the eye. Mathis, on the corner of #37, is only about 20 miles further. The station at Mathis was really upgraded to a full Shell station but last I checked the rest rooms were the same-o-same-o "art dreco." I'd give it a C-.
It's a relatively short haul to Robstown, which has a giant truck stop on the south side. Now this place is good, safe, and clean. You're over half way to Padre now. I'd refrain from talking with the truckers, though, since they're a tough bunch.
From here going south your pit stop potential goes way down. Get some gas soom if you lave less than a half of a tank, since it takes about 80 miles to get through King Ranch County, where there's nothing but cows. Bishop, Driscoll, and Kingsville are acceptable but watch out, the cops seem to like the revenue from speeding tickets along here.
There's one mention of note in Kingsville, the L&M Superette. The cops go here; the post office trucks stop here; and Border Patrol stops here; the truckers stop there. But this place had the most god-awful restrooms I have ever seen. People were running out the front door with the hands over their mouths. Hopefully, the new owner is fixing up the poor place.
We always stop at the Department of Transportation rest stop south of Sarita, which is a few miles north of the Border Patrol check-stop. You'll see a lot of people stopping there after going through the check-point on their way north ... and trying real hard to look cool! Some were pretty darned close to being deported or busted. Just remember YOU have to go back through the same check-point if you drive back from the beach. Fortunately, you get a bye and there's no K-9 Border Check headed south. Sorta needed to stop, didn't, and need to turn back? I'd suggest it because this place, while it has high traffic, is very clean and there's nothing until Raymondville, unless you do the boy-thing along the side of the road (not recommended). Use the turn-arounds, which were built for silly people just like you and me.
Yup, there's the McDonalds in Raymondville and the further south you go the better the options get. The construction on #77 is real bad so be careful, stay on the main road (don't end up going to McAllen), drive slow, and keep going if at all possible. When you see the Valley Distribution Company on the right, the purveyors of most all the local beer products (hee-haw!), it is time to hook up with Route 100.
Just as you hang a louie (a left) you'll see a citrus fruit stand. Now this place is good and we usually make it all the way to the Island from here. Very clean. Plus, they have beer, ice cream, and ... oh I forgot, tons of oranges, grapefruits, lemons and fresh juices. Hey, a little vitamin C isn't going to hurt you. Try mixing their fresh juices with the booze of your choice and you'll notice the difference right away.
You'll be passing Los Fresnos and some other town with OK pit-stop potential; we always plug further on down the road watch that speedomoter like a hawk. Yes, this is Speed Trap City. Sometimes we get so excited after leaving Los Fresnos in the rear-view mirror we crack open some brewskies ... so by the time we get to Port Isabelle, mama's bladder if doing the wild thing again. There are plenty of alternatives but our favorite is B&A Seafood, on the left just before the bridges. We really like B&A and to their credit, this restroom is consistently the cleanest of any we have ever seen on any of our trips. Get freaky and buy a pound or two of shrimp - ya gotta be pretty lame if you can't boil water, right? Head up the towards the bridge and smile. Relax: you're on the island now.
I hope you liked my little pit-stop guide. Over the years, many have gone out of business and you'll see their dinosaur bones on the side of the road. It is almost like time-traveling.