At any given time I am working on 5 or ten different sets. I find one or two (or more if I get really lucky) each trip. I bring a piece of cardboard with the sets with the missing pins, but not my completed sets. and then I make a note in my phone about which ones I need. I only bring traders into the parks so I don't risk losing ones I plan to keep (it happened before and it took me the whole trip to re-find one I had dropped somewhere). These are the ones I need to find on our next trip for example.
Dwarf boxes- need Happy
WOC sprayer- need light blue
Snowflake- jiminy/fauna/flora
Cauldron- Hook/Hag
And then of course I bring the traders and extra backs. Invariably I find another set or two or three that I love and add those to the list. And if I find a good deal on new traders (coupon on cs receipt for example or cheap purchase with purchase.) I will buy a few new traders as well.