If you're batoning 2"-4" logs with a 4-6" knife, you're probably ok with a 8"-10"- bladed saw... Bahco makes one called the Laplander that's perfect. The Fiskars pruning saw is also nice, though mine only works on the pull stroke, which drives me nuts. For the connoisseur, Silky makes wonderful saws (though pricey).
If you're using a hatchet and processing wood 6"-8" thick, a folding 24" bucksaw would be a better choice.