Three items?
1. My HTC Incredible, I ended up getting mine for free at signing due to some stuff, which was awesome, but it's my one thing I need to carry most of the time. It's my alarm clock, my calendar, my email, my only phone. I use it to check out wireless networks, find my way to places in other cities, it mutes when i get to work, but is on loud when I get home, it's just my multitool for everything.
2. My Timbuk2 messenger bag. I know it's not the most ergonomic bag, and I was lucky to get one before timbuk2 became big and the quality of their materials dropped. When I bought it I was going through 2 or 3 backpacks a year at school. I've had that one bag for the last 6 or 7 years, and the only damage it's taken is that one of the Velcro pads on the inside of the bag has come off. I really wish I had spent more money on it when I bought it the first time, but I'm more than happy with it now. I've looked into buying a second one of a larger size for weekend getaways and such, but haven't convinced myself i need it.
3. Good sheets/Matress Topper. It's amazing the difference between $20 and $50 sheets. When I moved into an actual house in college and got my bed from my old house, I had nice sheets my parents bought when i was a kid that lasted 4 or 5 years and were still incredibly comfortable. About a year after that i wore through the fitted sheet and went out and got a $20 sheet set. That set died within 6 months. I got an internship, and actually had money, so i bought around $100 in new sheets, and a new mattress topper, and it's made a world of difference.