Buckets fit into milk crates. Could you connect two milk crates to extend a base board  (( 1X3 on each side of crate)) to extend outside of the sled  half the size of milk crates on each side.

The milk creates will carry the bucket. In the extra space of the square you can carry  and ice scope , tip ups and rods and minnow buckets.  Could hold the base boards with pungees or wing nut through rim of sled. Would still leave room under the base board for more items