I wouldn't recommend jeans, they soak in water like no mans business and don't dry out easy.
I wear moleskins and a pair of Barbour waxed over trousers / chaps.
When I was a kid I just used to wear a pair of army trousers.
End of the day you can pretty much wear what you want but just remember, your gunna be walking in them near enough all day, weather could turn hot then cold, even if it ain't raining at the time, walking though a bit of beat that was rained on the day or night before is gunna get you wet.