So long as you're warm, we're happy! Blazers, tie or no tie, hiking shoes or flats, dresses with leggings, blanket scarves, jackets and fascinators all acceptable :)
If you'll be drinking with us we recommend taking a Lyft or Uber, although cell service can be a bit spotty for non-Verizon folks. The Roberts parking lot supposedly fills up around 1pm, so feel free to come early and enjoy the lawn games or the hiking. Some street parking and spots at the Chabot Space Center may also be available (about a 20 minute walk away).
Yourselves (and your layers). We'll have trunk "coat checks" for those without vehicles. No valuables that might get wandered away from please, and since it's a public park it's important to not leave anything tempting in sight your vehicle.