I can't see James with a job at all. If it hadn't been for the war, then I could see him wanting to play Quidditch, or do something fun. It's not as if he needs the money, so it would be something to keep him occupied.

Remember that the Order was smaller during the first war (Remus says as much at the beginning of OOTP when Molly's crying over the Boggart). James wouldn't have had time to work unless it was necessary for the Order. For instance, I have Peter working at the Ministry and the order because he needs the money and the job could be useful, but James doesn't have that need.

if you don't like him being unemployed then why not try him having a hobby that consumes his spare time. Quidditch stats? Broomstick design?