I actually have a model I call the trail knife, but it's a personal definition.
A trail knife, I think, is a jack of all trades, so I tend to prefer- depending on environment- a 4.5 to 7.5 inch blade, generally light enough and thin enough for food prep work, but tough enough for casual batoning and light chopping.
taking a look at the more common WSS custom makers is probably a very good bet (do we have a list?). Import leukus and larger puukkos are a favorite around here, also.
While I don't want to open the can of worms too far, I'll add some of what I consider to be design condiserations of a trail knife:
1.ability to slice foods reasonably well
2.Nimbleness and ergonomics of the handle allowing fine work
3.light chopping
4.light batoning
5.whittlin or carving
6.critter defense
3,4 and 6 argue in favor of the 5-7 inch blade range, as does 1 to some extent. The rest argue for a large handled, but short bladed knife in the 2.5 to 4 inch range. Keeping a longer blade at a fairly thin spine and will a good slicing geometry and a well fitted handle offsets a lot of that- a larger blade that's designed properly can handel the small tasks safely and efficiently.