hi pposey, not sure if you are female/male, but here are some non-gender specific suggestions. here is a long answer.
Before you even think about buying, I hope you know how to bargain hard.
Coffee, get lots of it!!! A lot cheaper than buying it in Starbucks!! Roasted or unroasted. I like the unroasted beans because its fresher when you roast it yourself and your house will smell great. (be careful with the smoke detector though.)
Jewelry, especially silver. Gold is ridiculously expensive these days so unless you see something that you absolutely have to have (really!!) don't buy any. Hand-woven cotton fabrics are fantastic with embroidery (shirts, dresses, etc), and crosses (metal, wood, and printed or embroidered on textile). T-shirts with Ethiopian Art. For wood furniture you should probably get them in Rwanda. Quality and workmanship would probably be better there. If you live anywhere where you have cold winters, you MUST get a "gabbi" from Ethiopia. Its a hand-woven 100% cotton blanket/throw that you can use as a regular blanket or just to put on while you watch TV or read. It gets softer with age/washing and is, in my humble opinion, the best thing you can get in Ethiopia. I’m sure you can’t find one Ethiopian/Eritrean who doesn’t have one...myself included :-) Its cheap, around US$10–$12, lasts forever, and even comes with embroidery on the ends or just plain. You will not regret this buy, whether you are a man or a woman. They make scarves of the same material too in several different colors. Fantastic gifts for family/friends or for yourself. There are tons of cheap/inexpensive art that you can get and frame it once you get home. Not sure what you can get in Rwanda but Ethiopian art is typically different from art from most African countries.
You can also get some hand-made baskets. They can be used for decoration or functional (serving food) and come in all sizes.
If you have space, get a small clay pot/pan. Make sure it is “prepared” for cooking. There is usually a process that clay pots go through before they are used for cooking. The process is called “mamwashet” in Amharic. Its usually done by the person who buys the pots after they get it home. Maybe they can explain the process to you and you can do it. Its VERY simple. Or send me IM and I will tell you. You can use the pots on a gas stove or coal fire when you get home. Makes anything you cook in it delicious. Its cheap in Ethiopia. Just make sure you check it thoroughly for cracks and chips.
Pretty much everything you buy in Ethiopia is hand-made. Just bargain well and if you go to Merkato, be extra careful about your pockets/bag. And have fun taking in the chaos…it’s a fascinating place.