I'm guessing the OP is trying to figure out things to source and sell on a regular basis and I just don't see it in books/DVDs/PC games. They're an over-saturated commodity right now and it's a race to the bottom on pricing unless you want to sit on them for a REAL long time.
I've personally not had much luck with things like scary movie lots around Halloween because the shipping bones you to death even on a flat rate box compared to what people want to pay. I dunno though, maybe someone else is making a killing off fat stacks of garage sale DVDs they bought in huge bundles at a dime each - but it didn't seem like it was worth the hassle to me.
And cellphones - I tried a 5-ish year old Galaxy a few times and it didn't hardly even get any looks. A guy at work upgraded his phone early and had me put his year old LG Android phone on eBay since he didn't know how to do it. He wanted to get like $50 out of it and it managed to bring in about $250. I've had local lowball offers on my old stuff and usually can at least double it on the bay... which again, is highly unusual.

I'd say the sweet spot is an iPhone or a relatively popular Android within the last two years. It would ideally be an unlocked phone, but most people don't buy directly from the manufacturer so I'd stick with big carriers like Verizon, ATT, Sprint, or T-Mobile. Make sure it works well, it's factory reset, the sim card is pulled, and the serial number isn't blacklisted.
And while I'm writing a wall of text, I'll preach the virtues of brand name clothing. That crap is everywhere in thrift stores and garage sales. If you can grab some Air Jordans or Under Armour hoodies that are in great shape for less than a buck, you could probably sell most of it for at least $10 on eBay - and they aren't fragile like a Saturn game so your packaging costs/methods don't need to be up to our standards either. I've seen a dude on Youtube that hovers around Ross stores for hours with an Amazon app on his phone and digs through their mountains of garbage to grab piles of Nike sports bras and high margin basketball sneakers - and they probably fetch more because they're new.