Slippy on/in a kayak isn't an issue. Its not like its a boat and you're standing.
As to what you wear on your feet there are a lot of choices. I use a kayak in many different environments so for me I need a very versatile boot that provides both support and protection. It also has to allow me to hop up on rocky reefs, etc. and allow me not to kill my self. What I wear besides the boots depends upon the time of year and water temps. In warm weather its shorts and boots. When its cooler its breathable, stockingfoot waders and boots over them. After a few years of doing this I'm now using the same boots for both. They are the NRS Workboot. They have a terrific sole an no zipper. Zippers need care to function properly when subjected to sand, etc. I don't like to maintain things. I like them to work with minimal attention from me so now I'm zipperless and very pleased.