For field use, carrying the rifle and all you other gear is one of the most important considerations. Ive just ordered a "drag bag" that can be worn as a back pack with the rifle and everything else in it. Ive been down the sling route and decided that it sux. I even had one of the fancy 2 shoulder types... Plus you need a back pack anyways for water and binoculars, LRF, a bit of food GPS/PDA, ammo, blah blah blah...
As for a scope level, i ordered one off Sinclair international, the "offset scope level" i think its called so it can be easily seen from my other eye whilst looking thru the scope and without shifting my cheek weld, good price too.
Heaps of info on here, try using the search function, just about everything has been covered on here before.
Good luck