This isn't a highchair, but since you use it with one, I'm putting here. It doesn't really have a category that's a good fit.
I ordered my first package of these Table Toppers when my son began eating solid food from a highchair. They have made going out to dinner with him so much easier. If you don't know what they are, they are large, disposable, plastic mats that stick to the table for babies and toddlers to eat off of. They provide a clean surface to put your child's food on so you don't have to worry about their food dropping onto sticky, germy tables or even clean ones that have a coating of windex or some other chemical on them.
When I was trying to find something for this purpose I also looked at reuseable mats that you can clean, but I just didn't want to have to put a sticky, messy mat into my diaper bag whenever I left a restaurant. These are so much easier. You just unstick them and throw them away. I also like that these fold up easily and I can just keep a bunch in my bag. It's one less thing to remember when I am getting ready to go out to eat. They were great during the stage when every dish got thrown on the floor. We just skipped the dishes and put the food right on the mat. Now that he uses dishes, they are great for catching spilled food and containing the mess.
They are a little pricey, but they are also really big, so I cut mine in half when I get them. Voila...40 mats instead of 20!
When we eat at home we have reuseable mats, but these are great when we are out to dinner. I think they really make life easier.