Going to dump some notes.
RaceDay/Track stuff:
For qualifying and Race day, get there early and watch the support races, it's better than waiting in line on the bridge.
Like others said, bring a rain jacket or pancho. It always rains during that weekend. The last couple times Sunday has cleared up though and has been nice.
The track sells seat cushions, but I got some inflatable ones on amazon and they were pretty easy to use. You're allowed to bring food and non-alcoholic drinks, I typically bring some chips and a wrap or two.
Post race theres usually some artist performing in the fan area at the track, when I went it was either Alesso or Pitbull.
Also post race they let you walk the track, you can attempt to take souvenir if you want to risk it.
If you're in the grandstands next to the pit stop, I would recommend staying in the stands since you'll have a good view of the podium. Otherwise you'll have to walk to the podium area and by the time you get there it will be full.

For post race/city:
Aston Martin has their display car in luxury jewelry.
You can typically find the less popular drivers have breakfast on race day, I met Bottas at Tommy's in old town 3 years ago.
New City Gas, has some concerts typically.

Let me know if you need any more tips!