I like to use different types of yarn, and, if possible, organic yarn. I love to shop yarn when I travel and I can spend hours in a yarn shop. In my patterns you will find information about the yarn I have used, and I use Ravelry´s information about thickness, so you can always find alternatives to the yarn I have used.
I save all kinds of scrap yarn, even the shortest bits of threads, to use in later projects. The shortest ones I save in a bag to use as filling in for example Christmas decorations. The longer ones are used to knit or crochet scrap yarn clothes or other items.
I don´t have the heart to throw away anything handmade, so I save up to make cushions, afghans, clothes and pots. I have more ideas than time (I guess that goes for all of us) but I will share patterns as soon as I finish projects.
Here are charts for the sizes I use.