Yarn: Premature babies have very delicate skin and can often be allergic to wool; therefore it is best to steer clear of garments made with a wool mix. Acrylic yarn is more appropriate when knitting for preemies. Ideal yarn to use for preemie knits is baby double knit or 4ply yarn. Most preemie patterns will use these.
Other smaller accessories that can be particularly useful when working on a knitting project are stitch markers, which can be used to mark particular points in a pattern that you are working on. These often come in the form of small rings which can simply be slipped onto your knitting needles as you knit.
Fastenings: Plain flat half-inch buttons are best to use for fastening. Avoid nylon and metal fastenings, as they get very hot under the incubator heaters. Do not use Velcro as a fastening, it is very scratchy on the hook side and also damages knitted garments when they are laundered. Ease of dressing is vital for preemies and as a general rule it is best not to use ribbon as a fastening as ribbon can often be fussy to tie on a garment so small.
Color Outside the Lines: I remember coloring books, and how careful I was to never get the crayon color outside the area I was coloring in or it would be ruined. Not so with knitting. Especially with scarf knitting. Because of all of the yarn choices we have, putting together beautifully color-crafted scarves is so easy. And so fun.
Finally, one essential accessory to keep your equipment safe is a set of knitting needle caps, which are designed to be placed over the end of your needles when they are not in use. As mentioned above, needles can cause damage to bags that they are kept in, and can even prove a safety hazard, especially if they fall into the hands of children.