Those places are still there. Although, I don't remember if Frontier Donuts still goes by that name, but they still do sell donuts.
As for E3, it's worth going at least once in your life.
You're probably aware of these tips, but just in case:
Wear comfortable shoes. Your feet will thank you.
If it is hot outside. bring a thin jacket anyway for the inside since they blast the A/C in the convention center.
Bring a backpack as they will have quite a bit of swag to give out and also so you can bring snacks/drinks with you.
Make sure to have plenty of cash for parking/food as this year's parking was $25 a day at the LACC or better yet, take the Metro.
Check for E3 parties 1-3 months before the event and register to all of them if you can(invite only and registered attendee parties) as you will most likely be party hopping the entire week(if you're staying local to the con center).
Your E3 badge can sometimes get you free food outside of the con center and also across the street with participating food trucks/tents.
Bring your I.D. with you as they check quite often if your I.D. matches your badge every time you re-enter the West, South, Concourse hall, and Meeting rooms.
Anyway, good luck.