One of the more convenient ways, I've found, to chum from a kayak is to use a lobsterman's baitbag.
Chop up the herring onshore into say 1/4" bits and fill the bait bag. Paddle out to your spot. The bag can then be hung over the side to create a slick. Meanwhile, bits and pieces of the herring fall out of the mesh and create a chum cloud. Come time to chum in earnest, open the bag, remove chunks by the handful, and toss them.
If you want to bottom fish (flounder, cod, etc.), it's an easy to matter to stuff a few rocks into the bag with the chum, sink the bag to the bottom, and bang the bag up and down on the bottom flounder-pounder style.
I like using the lobsterman's chum bag for one because I can find them on most beaches in Mass. after noreast storms, for second because the bag keeps the chum out of my ****pit, out of my lap, thus creating less of a mess and stench. When the day's over, I tie the bag to the stern of my kayak for use as an overhang flag for the drive home.
Anybody use other techniques than this?