What I do when I have multiple travel funds is to buy a ticket with whatever funds I can without paying any additional cash. Then if I still have remaining funds, I wait a day and then change my ticket to a more expensive ticket. That way I slowly use up the travel funds without creating more funds. They goal is to get it down to one fund instead of multiple ones.
For example - I use two funds to buy a $49 ticket. Then I go back the next day or so and change the ticket to a $59 ticket or higher, in an attempt to use up all those remaining travel funds. The goal is to not use any new cash. I usually end up with a little remaining fund, which is fine.