I spent most of yesterday buying cheap items (20-30nps each) to make sure I'd have enough items to donate to reach my goal. Whew! It took a while, and ironically enough, I kept getting RE's that almost (if not completely) paid for all the purchases I made...mostly because I got one of the "Bank Error - reset interest" ones.
Now it's time to start going through them, as well as all the food items that are just hanging in my SDB.
JN's Guide has a list of dailies, battledome challengers, etc, that give qualifying R90+'s. I think they've got it pretty well covered. Except they left out that some of the wheels give out prizes, too...like the WoMon, which can give out R90+ foods.
I am actually going to change up who I battle for items for the next few days, thanks to their guide, and I totally only just now realized that the Brightvale Scrolls, which are battledome items, and thus I dismissed as not possible to use, apparently work. I'm kinda kicking myself for that, and celebrating at the same time. Kicking myself, because I have almost 900 of them, and thus could've purchased a LOT FEWER items yesterday, but celebrating, because that's another how many shots at rare stamps for avvies?
ETA: Well, it's essentially over (or will be in the next few hours). Apparently there's a new avvie, but if you got the avvie last time (in 2015), this one isn't working. Hopefully they'll award it post-event, since I can't stay up any later tonight to worry about it. I think with as many times as I donated, across all 7/8 days, I should qualify, but I guess we'll see.
Also, I spent more than half of what I had in my bank, buying things. Sigh. Hopefully some of the more expensive R90+ items I ended up with will start to sell soon, but while my bank account is hurting, I'm not really wanting to take super undercut offers on them, either. And goodness only knows how long it'll take to sell the morphing potions (which is what most of the R99 items I ended up with are). Ah well. Some day I'll learn, I shouldn't gamble on these things, I should just sell whatever I've got in my SDB and enjoy the profits from it. (This is why I stay away from Vegas in real life!)