What to pack for your first few nights in a tent, plus the site setup order that keeps a pitch from going sideways in the dark.
A tent rated for three is comfortable for two adults with gear. Manufacturer capacities assume shoulder to shoulder sleeping with nothing else inside, so sizing up one person is normal for car camping.
For car camping it mostly protects the floor from abrasion and is optional. If you use one, cut or fold it slightly smaller than the tent floor so rain does not collect between the two layers.
Almost always the pad. A bag insulates the air around you but compresses under your body, so the ground pulls heat unless an insulated pad sits between you and it. Check the R-value before you buy a warmer bag.
Follow the land manager rule for that specific place: a metal locker, an approved canister, or a hard sided vehicle. Never in the tent, even sealed snacks, and that includes toothpaste and trash.
Aim to be on site at least two hours before dark. That gives time to pitch, cook, and find the water spigot without a headlamp.
