I love Word Rings! Each student is given a loose leaf ring for their very own words. Every day they are given three index cards that I will write down any words of their choice. These are words they want to have on a card. Although I don't always do this - some years I have had the rule that they had to be able to read the words they have before they could get the next ones. It depends on the time I have to dedicate to this. :)
What I love about this process is that the students are taking ownership and these are the words that are meaningful to them. It can even become a challenge to see how many words they "have." Love it! I let the children be in charge of asking for more words. I like it to be totally "kid-driven" because if the process is to be meaningful - it will be from their desire for the cards. And honestly, most of the children eventually want one of those word rings!
I keep a stack of index cards (5 x 7) and a single hole punch ready to go!