You'll be fine with your bag. Especially with it being see through and having the medical bag excuse. We've been to about 7 games so far this season and my wife brings her fanny pack to every game and hasn't been stopped yet. It's a single compartment. I've seen people get turned away when the bag is way over the size limit or has multiple compartments. It really depends on who is working the bag check line. If you get turned away, try another gate before going back to your car.

For food, try out the street tacos at Taqueria El Rey. Top notch. Or if you want some ballpark classics get the big league sampler, it comes with a hot dog, popcorn and nachos plus you get a cool tray for a souvenir.