This is not helpful, but I went maybe 8-9 years ago and had a blast. The best was "tailgating" in one of the squares during the parade. Have fun!
Yes, no open container law in Savannah (except when driving obv.) If you have an adult beverage around downtown, it's OK as long as it's in a plastic cup. If you want to set up a party in one of the squares along the parade route (as Lady was referring to), be prepared to stake your claim EARLY on the morning of the parade. Many folks have their annual spots and basically camp out to get them.
Parking is a bitch, and the taxi situation after the bars close is a complete shitshow. If you're not staying within walking distance, be ready to either spend an hour just finding a cab, or steal a cab from an unfortunate soul who spent an hour just finding a cab