I cannot think of anything really nerdy to do in Riga, but make sure to walk in the old part of the town. It is beautiful. I can, however, give you some food and drink recommendations.
If you want to eat something Latvian, then visit a place called Lido. It is a chain of restaurants in Latvia that serves traditional Latvian food and there a few in the center of Riga. If you want to try the best burger money can by in Riga, you should visit Street Burger. It will cost you about 8 EUR for a burger, drink and fries and the burger is just good....just so good. I also recommend a kebab joint Pakistan Kebab. It is a bit hard to find, but it is near the central train station and they sell, what I think, are the best kebabs in the city.
For drinks you should go to a folk club "Ala" or Cave in English. They have the best selection of beer in the country and you can get there some of the more hard to find beers. If you want try something interesting tasting, ask for honey beer, hemp beer or cranberry beer. If you want something more traditional, ask for Brenguļu Beer or Valmiermuižas Beer. Those are some of the best beers I have tasted and both have a dark and light version (Brenguļu dark is a God's gift to us, puny mortals). Just make sure to visit it early in the evening, it can get very crowded. And there are plenty of regular ass nightclubs to be found, if you want to go that rout.
If you want, I can meet you in Riga and show you some of the places I talked about.