According to Neowing, each of the four volumes of Usagi Drop
Blu-ray & DVD will carry an extra short episode. The first volume will be released on October 28th.
Vol.1: Episode 2.5 "Aquarium of Leaves"
Vol.2: Episode 3.5 "Dear My Santa Claus"
Vol.3: Episode 6.5 "Full Blossom in the Sky"
Vol.4: Episode 8.5 "Way Home"
Usagi Drop Specials