I fish at night quite a bit, and that makes watching your rods a bit difficult especially if you don't use a lantern because of bugs. I have tried the lit bobbers but I like fishing deep and they drift into my other lines. I found some tiny glow sticks that are designed to clip on the end of rods but the initial cost is about $5 for several little plastic clips and one tiny glow stick.
I was cutting through the birthday card section of Wal-Mart and in the kids party favor area they have glow sticks and glow bracelets for 97 cents a 5 pack. They even have larger packs of 40, 65 and 100. The 100 pack is only $10.
I clipped them on my rods 2/3 of the way up and they don't mess with my casting.