When Caleb and I started registering for our wedding, we had no idea what we really needed beyond the typical stuff like a blender. After a few showers and a couple registries, I feel like we have a good idea of what you need when you're starting out as a couple - you need your basics, but you can register for fun stuff too!
1. A vacuum - I had a crappy Shark that served well enough for my place, but our new apartment needs something more heavy duty (especially with Margo shedding everywhere). Even if you're in a smaller space that may not need as much cleaning, go ahead and register for the nice things you'll need to clean an eventual house - this is the only time everyone will be lining up to buy you cleaning supplies!
2. A nice blender - You can get a little cheap one for like 20 bucks, but on your registry go for the more upscale versions. They make a wider variety of things and they'll last a lot longer. Go for the fancier versions with every small appliance you register for so that you won't have to replace them in a year - and this is one of the only times that you'll have takers for those bigger ticket items.
3. Dishes - If you're combining two households, you probably already have lots of dishes, but go ahead and register for some nicer ones. You'll want them later on, and then you'll have ones that go together rather than a modge podge.
4. Bedding - You'll definitely need it, and its a great opportunity to get some high thread count sheets :) We registered in neutral colors so that when we have a house we can actually paint, we won't have to buy new bedding to go with whatever colors we paint the master bedroom.
5. Camping Equipment (or other fun outdoorsy stuff) - This didn't even cross my mind until Caleb jacked the Target registry and registered for a bunch of outdoor equipment, but its completely acceptable to register for fun stuff! And your friends will be glad that you did; how much more fun is it to buy something like a tent or a bike than a microwave?
Which brings me to:
3 Things to Not Bother Registering For
1. A microwave - most apartments (and even some houses) come with them, and chances are at least one of you has one already. Some may look fancier than others, but unlike blenders, all microwaves pretty much do the same thing. I would much rather save this space on the registry for something else like flatware or dishes.
2. Throw pillows - these go in and out of style so quick that whichever ones you register for you probably won't like in a year. Plus, they'r really expensive for not a lot of utility. Save some money and make your own - then they'll be unique and more economical.
3. Anything with "His and Hers" on it - this is more of an opinion... but I just think its kinda tacky.