I bought a flock block one year and they enjoyed that. For a small flock (1/2 dozen perhaps) it lasted most of the winter. My flock is quite a bit larger now, with about 50 birds (chicken math at its finest) so I probably won't do a flock block again. I do buy suet blocks from time to time though, and offer those as a diversion every now and then.
Mine do have a yard large enough that it feels like free-range to them even though there are perimeter fences. I have found that they get out and about throughout the winter. Oh sure, the first time they see snow they won't step foot in it but after they get used to it, I'll see them out trudging through the snow. I almost always have pullets that are still laying, so that keeps them busy for awhile. And, I visit often. Whenever I visit the coop, I take them a warm mash (take warm water or the juice drained from peas, beans or corn, and add their crumbles or pellets, wait a second and it turns into mash). They seem to really enjoy the mashes and it makes me feel better to think I am warming them up with the warm food. Eating a big bowl of mash keeps them busy for a little while too.
So- what do YOU do to keep the winter peckies away? A cabbage head? Scratch? Store-bought greens to hold off the craving for well...greens? Your ideas here! 
