On YouTube I watched a video by a fellow named James Yeager about how there is no such thing as One Rifle for everything.  He calls it a myth. 
I call Bullshit on that.
History is full of instances where a man has just one rifle and did everything with it, just fine.  Survived to tell the tale.  James Yeager is free to express his own opinions, but he is not free to his own Facts.  US History, be it Frontier History, Western Expansion, Wild West, Military History… what ever kind of history you want to call it.  Only in our Modern Email Era do we enjoy having more than one rifle for different purposes. 
In this Modern Era, the late Colonel Jeff Cooper considered a One Rifle concept and called it the “Scout”.  His Scout Rifle Concept is a proven winner.  Steyr manufactured their Scout with Jeff’s blessing and assistance.  And it pretty much did what was promised.  Now Ruger and Savage are making Factory Scout Rifles with pretty good success.
Any one of these would make for a fine “One Rifle” solution. 
Historically, the One Rifle has been a Winchester Lever Action in .30-30, .32 Special or the like.  Today a good solid and smooth cycling Lever Action is truly a thing of joy.  There are few things you can’t do with a .30-30.  I’ve even killed an Elk with one at 200 yards, and I’m sure I’m not the only person in history to have done so.
Today’s Rifleman though is packing an AR.  The Black Rifle has gone mainstream… and for many new shooters, the AR is The One.  The AR-15 might be kind of light for a One Rifle, but an AR-10 type rifle gives you some considerable advantages in terminal performance on big game.
After some consideration, I’m thinking a new One Rifle is more than doable.    Let’s do that AR platform in .308.  Let’s hit it with a light weight, 16″ True Polygonal Rifled Barrel, and let’s give it some lightweight furniture with an adjustable stock.   Simple, Clean, and effective in most any situation.  Give it an adjustable 1-4 power optic.  Give it a tough finish, resistant to abrasion and corrosion. 
Contact CrusaderWeaponry.com to order you a Crusader One Rifle.