You select a more-items boost from the boost screen, which generally appears just prior to starting a game. The more-items boost will usually make additional items available for collections in the game. However, you don’t know in advance how many items were expected to be played without the boost. The number of collection items in any given game is random. This means that, if your next game is expected to have 1 collection item, then using a more-items boost might simply add 1 additional item, giving you only 2 total items to collect in that game. So, I generally only use the more-items boost to clear a goal. I don’t usually use it in hopes of collecting specific items.