Pleasant summer knitting are bookmarks. They are nicely portable, carry the satisfaction of completion in one sitting, and make wonderful gifts that can be enclosed in a card or become the front of a card (tacked on with a few stitches) for knitters and readers. This is also an opportunity to try all different kinds of fibre: paper string, ribbon, soy, hemp, handpainted wool, decorative yarn, bamboo, the small amounts of wool left over from knitting projects (and these, then, become reminders and memories of the sweater or afghan or socks).
Here is one example: personalize it as you wish.
From Mary Thomas’s Book OF Knitting Patterns, Lace Faggot Chain
Cast on twelve stitches
lst row K2 *P2tog with yarn in back of work (from *4 times) K2 (12sts)
2nd row Knit
Continue until desired length.
Next row K2 tog across (6 times) (6sts)
Next row Knit
Next row K2 tog across (3 times) (3 sts)
Next row K2tog K1
Next row K2tog Put yarn through stitch to finish.
Now crochet a tail of single crochet to desired length (to hang out of book) and either crochet something interesting at the end or hang a bead or make a decorative knot.