1. I find things that I've forgotten that I had in the first place, that's quite nice, especially when you find maybe money or, I ____, a voucher or something. 2. At the moment, just looking around, there are so many things that I ____ to tidy up.

I don’t know
Полное предложение: “…especially when you find maybe money or, I don’t know, a voucher or something.”
Здесь I don’t know используется как разговорная вставка: «ну, например», «не знаю, какой-нибудь ваучер».

need
Полное предложение: “There are so many things that I need to tidy up.”
Need to tidy up означает «нужно прибрать / привести в порядок».