Does anyone know which items in the Cash Shop give a bonus item if bought together? I figure this will be helpful for others possibly..

I know so far: Chibi Plushies Chilly Teddy Snowglobes

White Fox Companion (wearable) is given when you buy a mess of snowglobes. If you want to see all of them go to Subetalodge and type "given" in the Notes section and limit rarity to 150 only.

This doesn't reveal the bonuses to your two sets, so there might be more sets besides these three. Try whatever you got from your two sets into their Item Database and see what the Notes say about it and then try to duplicate keywords from that.