If you use a leash, it is best to have a harness for the cat, not just a collar. Cats are very good at squeezing out of collars in a snap. I would hate to think you are walking a cat by a gas station with cars whizzing by. The poor cat would be scared out of it's wits!
A trip of your length should not require that a cat be walked outside anyway. The little thing would probably hate it! A cage large enough for a litter box with a bed overhead would be ideal.