I’m sure your father’s already told you, but just in case: Is there anything in Santee other than strip malls? (And the women’s prison?)
As for daytime sights, try a drive to the Cabrillo monument, going through Ft. Rosecrans military cemetery. (Check its hours to make sure the old lighthouse is open when you go there.) On the way or back, there’s a public beach that’s so obscure it’s essentially private for those that know about it, and who are almost exclusively folks from the neighborhood. (Send a PM for directions.)
As for Old Town, I know that place pretty well, since as a teenager I worked for four years in one of its more well-known (Mexican) restaurants, which my step-mother owns. (Being from West Texas, you’re probably not looking for Mexican food while in San Diego anyway, and there’s no reason why you’d have to go to Old Town for it, but it wouldn’t be my former workplace there that I’d recommend.) Instead, go to the Old Town Mexican Café, which you might try for lunch before the game. While there, if you’re interested in the historical stuff in the state park, I’d recommend Campo Santo, the oldest European cemetery in the state (which is not actually in the park, but a block or two from OTMC). The cemetery itself was moved about 30 feet, so the actual graves are underneath San Diego Ave. and its sidewalk (with markers), but you can see the gravestones etc. nearby. There’s also a good museum across the street from the trolley (which will show you how similar the city’s history is to that of west Texas, in that it was a cattle-ranching economy). I’d say all of this would be preferable to enduring that annoying mutation of the human species known as Charger fans, who congregate in the parking lot of Qualcom before each game to tailgate.
When you go to La Jolla, include a drive up to the top of Mt. Soledad if it’s a clear day on the coast, and it usually is in Oct. Before you go you might want to read about the eternal and pointless controversy regarding the cross up there.
And if you visit Coronado, by all means check out the Hotel del, but don’t eat there. Save some money and have a better lunch across the street at Vino’s café, in the Hotel Cordova.
Some here have recommended the Gaslamp, but with all due respect, I wouldn’t put it very high on my list. Don’t be fooled by its would-be, pseudo-historical Main Street Disneyland style name. The only history belonging to the Gaslamp is that when your father left San Diego its most useful purpose was to provide sailors with prostitutes and tattoos. The city boosterists (who are constantly throwing money at their developer friends) convinced the city that it had some kind of historic value, so they closed down the flop houses, threw out the whores, spruced up the buildings, and now tourists flock there because because their tour guides tell them to. You can spend your money on over-priced and over-rated, corporate-owned restaurants and nightclubs anywhere in the country, and—unless you have a specific recommendation from a personal source–there isn’t any particular reason why you need to do so in the Gaslamp, unless there’s a theater nearby you’re going to anyway.
Instead, you might consider a night in Pacific Beach, which is more organic and less a tourist trap. Check it out on Saturday night: look into the live music there (in the local weekly), and get a designated driver or take a cab from Little Italy to check out whatever various places might interest you. (Just keep your eyes off of women who “belong” to other guys.)
As for Balboa Park, go there on Tuesday afternoon and evening. A quarter of the museums will have free entrance (find out which ones in advance), and by that time the Haunted Trail will be open for the Halloween season.
And if your Wednesday afternoon is free, go to Ocean Beach during the weekly farmers’ market, just to see that the city doesn’t consist entirely of bleached blondes and fat guys in shorts and tank-tops. There you can have lunch at the café on the pier, or at Poma’s Italian sandwich shop, and happily ignore the food on the plane back to Texas.