If you're looking for a meeting place or a good stop around ½ or halfway between San Antonio and Corpus Christi, you can try Three Rivers, TX, which is about 1 hour south of San Antonio, or about 1 hour northwest of Corpus Christi.
Other possible places to stop near the midpoint include Ray Point, and Oakville.
About ⅓ or a third of the way, you can stop at Leal, TX. This is about half an hour south of San Antonio.
About ⅔ or two thirds of the way, you can stop at Dinero, TX. This is about 1½ hours south of San Antonio, or almost an hour northwest of Corpus Christi.
About ¾ or three fourths of the way, you can stop at Lakewood Heights, TX. This is about 1½ hours southeast of San Antonio, or about half an hour northwest of Corpus Christi.
If you drive straight through without stopping at all, the total distance is 143 miles. The distances shown above don't include local roads to get into each town, so if you're planning a long road trip, make sure you factor in traffic and road conditions, rest stop breaks, and interesting detours along the way. If you're in a rush, you can do the trip with zero stops, and your total travel time would be around 2 hours, 4 minutes.