I think if you are going to serve food or alcohol on their property, then you may need to partner with these bar/restaurants and have the benefit of their restaurant and liquor licenses to be in compliance with local laws. Essentially you can't just roll into town, and open up an unregulated food truck. You may need to purchase all food and drink from them and pay their employees to serve and check IDs.
Now if you are talking about more of a tailgate party, say at a stadium parking lot or similar, then you can probably cordon off space, bring your
own supplies, and let your email blast tell people where to find you.
Agree to let the alumni help you.