calorie count for change in daily activity

beefolks

During the week, my activity level is best described as "office worker" - computer work, some heavy lifting, but not super active for the most part. However, on weekends, I work at street festivals. On these days, I am on my feet, constantly moving and stretching, setting up and tearing down a canvas tent, restocking the table, etc., for 10-18 hours straight. I feel I should account for a caloric difference, but I don't know what value to use. Any suggestions?