If you're thinking a leather strop for your round knife, etc., I use jeweller's rouge mixed with a bit of olive oil (to make it stick) rubbed onto the leather.
Something like this (only connection with seller was as a satisfied customer):
http://www.ebay.co.uk/itm/JEWELLERS...ewelleryBoxes_Supplies_CA&hash=item3a597bdf16 TBH, 50g or even 25g ought to be plenty, but 100g will see me out.
If you have a hollow back edge shave, there's a video on the Tandy site about how to make a strop for that (and general leather tool sharpening)
Just remember to wipe the tool (and wash your hands) after stropping! You don't want red marks on that lovely clean leather!.
Geoff