I was always onto this mindset in all my life. If I crave something for atleast 1-2 week I probably need it. For example playing VR always pops into my mind so I definitely need a VR headset.
EDIT: There was one cheap thing that was really "useful" for me. My school had a merch shop where they sold pens with rubber onto it. With this I was able to play Hearthstone on my phone while class.