Corks are great craft items for building a large number of projects. You get your corks in a fun manner - by drinking wine! Here is some basic information when creating crafts out of cork.
First, most wine bottles have a standard internal neck size. That is 3/4". So pretty much any cork you get will be 3/4" wide.
On the other hand, corks range between 1 1/2" to 2" long or more. That 1/2" might not seem a lot of difference, but it can create huge problems if you are trying to create grids of corks. Be sure to sort out your corks by their length, so you can account for this.
Cork is a spongy material that can get mouldy. Normally, cork shouldn't be used for outside uses. It is a great blocker of heat, so it works wonderfully for trivets and trays. It can be spraypainted for decorative uses. Most people know about "corkboards" - and wine corks do a great job in this application.