What prescription or over-the-counter therapies have you found effective for helping vitiligo patients cover active areas?  

As Dr. @Tran mentioned, selecting the correct topical steroid strength based on location is important. We have had patients make great progress (even without nbUVB therapy / xTrac) by alternating every 1-2 weeks with a topical steroid and a non-steroidal (i.e., Pimecrolimus cream or Tacrolimus oint...

I start with topical corticosteroids strength based on body location. I also alternate with pro topic or elidel. There is a new topical jak inhibitor that got approved that I would consider trying in the future but I have no experience with it yet. 

I use a strong topical steroid (almost regardless of body site) BID 7-10 days a month, and tacrolimus 0.1 BID every day of the month. Reevaluate 3-4 months later. Opzelura now may change that, but recently denied by Medi-Cal as cosmetic.