I just bought this new bag: 
  https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1 
I am excited to use it as I am overdue for a new one - our current bag is literally falling apart lol. I'll give a review on it once I get it.  
 But for road trips, I like to be extra prepared in case I decided to stay longer or whatever the case may be.  
So I always bring their regular food for meals as well as some treats.
- Poop bags
- Wipes
- Multiple types of leashes (usually a Flexi for each, a 4ft and a 6ft, for different occasions lol)
- Extra harness just in case one malfunctions or is lost. 
- Collar and tags
- Water jug and water sprayer stays in the back of my car usually
- Bed possibly
- Car seat
- Travel bowls for water or food