Right of the top I would recommend the double burger/ extra bun trick. (Order an extra bun and I think it costs about .79 or so.) Makes splitting burgers simple
Also, Peco's Bills has a very good chicken wrap that is huge, and I believe comes already cut in two.
Tusker House, & Cosmic Rays both have 1/2 chicken plates.
Basically, anything that is a sandwich could be easily split I would think.