I work fulltime and co-lead a troop. The key is to keep the number of girls manageable (10-12 max) and utilize your parents. Our troop has 10 girls and four of the moms have gone through the training. We have one offiicial leader, as required, but because we've all been trained, we can take a meeting or two a year for her. We sit down together twice a year and plan out a tentative schedule and pick the meetings we want to be in charge of (including getting the supplies together, etc.). We meet twice a month nine months of the year, so only 18 meetings total, some of which we devote to field trips, cookie sales, etc.
There are lots of good activity ideas in the handbook and online.
The ones our girls like best: crafts, crafts, crafts; mock slumber party with karaoke and make your own pizza; sports day (set up at a park with different stations: shoot a basket, walk a line, shoot a goal); manners meeting (pass the teacup, place setting relay, phone etiquette, make believe restaurant)
These were all really easy!!!
We've found many free field trips, etc. Petco, grocery store, local pizza place, candy factory, farm. We find a tryit that the trip somewhat matches, and voila, easy meeting with part of a tryit earned.
Also, we toyed with the idea of assigning each girl a meeting to be in charge of craft instead of dividing up snack, but since we had so many moms involved, we didn't need to.
Good luck!
Just remember, you do not have to be a commando leader. The girls will get just as much out of a low key group and you will not burn out as quickly.