A tldr guide for CC is essentially they give us categories of items (i.e. books, petpets, foods, scrolls, etc) and then if you donate items within certain ranges, then you get a random item from that same range. For instance, if you donate 5 r90-r99 items, you can get a random r90-r99 item including things like BGC, stamps, etc. What happens is donation items eventually inflate to insane amounts due to the potential profit from getting a lot of random r99 items or getting one big ticket item (like an avatar R99 stamp such as BSS or something).