Beaver Head and Feet

[Skweres]

the tail hanging off the back would be pretty awesome, specially with the head as the flap

[Wompet]

Some of the beavers I've seen were big enough that their tails would have made decent sized sporrans.
Without seeing the size of the pelt: mask as lid, feet as tassels, remainder of the pelt as front of sporran, and leather for the back and gusset.

[way2fractious]

I agree with Wompet, who agrees with your idea - a brown leather sporran, adorned with whatever pieces of the pelt you have. To me, that would be a mark of a true conservator of the natural environment and its resources.