Depending on where I am going and how long I plan to be out, this is typically what I would pack for a day's shooting with the large format kit.
All of this fits into my backpack which is a Naneu Pro KL3. I'm not sure if these are still on the market but I really like this one. It has a laptop sleeve which is perfect for storing dark slides. As well as a hip strap, the backpack features a suspended, mesh screen that prevents the pack coming into contact with your back. This makes lugging a heavy kit around so much easier, especially in hot weather. The material is tear and weather resistant and it has a separate rain cover.
In addition to the items listed below I'll usually carry at least one water bottle/bag, sometimes a small thermos of coffee (sometimes a hip flask), a couple of protein bars, sandwiches if I'll be gone all day, and some spare batteries for the light meter. These days I usually have a mask stuffed in there as well.
In the car I will always keep a pair of rain pants, a towel, dry shoes and socks, a pair of tracksuit pants, and a spare tee shirt in a bag. I keep a couple of spare bags as well for my dirty clothes or muddy boots. I've learned from experience that it's well worth the trouble of packing this stuff.