Traffic heading into Quartzsite can and does back up, but really only the first two days of the Big Tent event. Most times there is heavier traffic but it clears out soon. Backups on Highway 95 to the stoplights can be for several miles in the mornings of the big tent week. Afternoons it is less as folks clear out.
Arrive when you wish. I would suggest either come just before the tent show opens or wait until midweek to hit less traffic and people in the tent.
Quartzsite has two small grocery stores and several Dollar stores with limited food. We stock up before we arrive but you can get most of what you need. Meats and fresh produce can be a little difficult or higher in price.
One of our favorite restaurants in The Laundromat restaurant - really. Right on main street and attached to the large Laundromat. Good food and good prices. Showers can be done in the laundromat with private, clean stalls and $6(??) for 20 minutes. A one stop place! LOL