One-on-one time with kiddos

I try to spend some one-on-one time with each of my kids 2-3 times a month, but I find that it can be challenging to work that into our busy family schedule! I picked my son up from school during his lunch break recently and took him out to eat. That was fun, but not something I can work into the budget on a weekly basis. Any suggestions out there for fitting "dates" with kids into the schedule?