Bring something warm, just in case, even if you're coming in the summer. It's surprising how long into the late Spring it stays cool at night.
If you're relying on public transit, it probably goes without saying that you should bring good walking shoes. Downtown is really fun to walk around, as is University Circle.
Toiletries and Medical Supplies: Buy bug repellant if coming in the summer
Photo Equipment: Cleveland is very photogenic and abounds with public parks and beautiful architecture. Not to even mention the lake. You may be surprised with how many pictures you take.
Luggage and bags:
I found out that I packed to many stuff, because clothes and everything is so cheap in USA, that you do not nedd to pack anything with you. You can buy everything you need right there....
One small bag is more that enouhg to pack.
You just have to go to one of many Outlet stores or Malls and you can buy anything you need.
...... Mall in Downtown Cleveland .....
Photo Equipment: Of course you must not forget your camera!!
Luggage and bags:
Bring an Umbrella and wear layered clothing
Miscellaneous: The weather can change and is quite variable so an umbrella and layer clothing may be a good idea. Since the area is near the Great Lakes rain is always a possiblity.
Since Cleveland is a Great Lakes city, the weather can change quickly and even the forecasters aren't *always* correct because it can be quite variable. So, you basically should bring clothing & outerwear/gear that will suit for differing conditions; check the forecats ahead of time; Channel 3 has the most accurate forecasts. One day the temps will may be in the 20's and the 60's F the next...
Photo Equipment: Maybe a tripod, because winds can be quite whipping and make still photos slightly tricky to get.
Camping/Beach/Outdoor Gear: Umbrella and windbreaker. Windbreaker mainly if you'll be downtown on a known windy day; the wind is oft faster than in Chicago; umbrella because we get a fair share of rain from the Lake-Effect wx systems.
Clothing/Shoes/Weather Gear: Well, this REALLY depends on when you plan on visiting! Monday it was in the low 20's F and very windy with lots of snow and today it is in the mid 40's F and wet and rainy. tomorrow we could drop to 0 F and in the summers it can get as hot as 100+. An umbrella is a good choice no matter what time of year and if you are wearing drss shoes, rubber covers are not a bad plan.