1. Skateboard: Well I don't skate anymore, I haven't for 4-5 years, but don't go cheap on skateboard stuff, a shit deck, wheels, trucks, and bearings will end up screwing you over into paying even more in the long run. Also learning skateboarding, you never want to learn how to skate on a Walmart board, you'll waste time and money. (Same for snowboarding, or any extreme sport for that matter, using a Walmart anything will never fill your needs)
2. PC headset: a shitty headset is never worth it.
3. CS:GO knives: don't settle for a BS Gut Knife Safari mesh, spend the extra cash and get the Karambit Sapphire.
4. Computer: Don't settle for a 100$ Chromebook, get a 2,000$ desktop!