1. The options must include one big bore double rifle (>.0.40), one large bore bolt action (0.375 and up) and one small bore bolt action (under 0.375).
3. Choices must include 3 rifles (no single rifle with switch-barrel configuration wizardry).Choices must be either rifles that you currently own or are within reasonable grasp of owning i.e. No Holland & Holland doubles unless you are that guy.
What would your trio include?
Because I'm a left-handed shooter, I'm a little more limited in my caliber selection (without going custom) than most shooters. I have some great selections in my safe for the small bore rifle but they're all falling block single shots so they don't meet the OP's requirements. Because of that restriction, I would choose my Steyr CL II in 30-06 for my small bore selection.
That might be a little larger than I would have wanted for the low end but it's a pretty versatile round with a solid reputation. I currently have this one setup to shoot a lighter 139gr bullet so that's probably a good alternative for the Ruger No. 1 RSI in 275 Rigby that I would have liked to have chosen for this spot.
My large bore rifle would be an African classic: A left-handed Winchester Model 70 Safari Express in 375 H&H (bottom).
If I wanted to, I could take the LH Sako 85 Hunter in 30-06 (top) instead of the previously chosen Steyr. Both of them are really nice rifles that I think would work equally well for plains game.
The big bore double >0.40 requirement is where I run into a bit of trouble since I don't currently own one (my LH Ruger M77 MkII in 458 Win Mag would be my big bore bolt choice). If I bought a used double, I might have to take a plane to the right-handed stock and shave it into a neutral one since I shoot ambidextrously (I prefer shooting left because of my less than perfect right eye not because I'm left-handed).
If I wanted to get a left-handed double, affordability would probably be a priority. Picking a specific caliber might not be an option if I'm buying used. Fortunately, all of the big rimmed >0.40 cartridges that I've looked at appear to be adequate for anything I plan to point a rifle at. So today, the choice would be a
left-handed Chapuis chambered in 470 Nitro Express for $10,500 for sale at Champlin Arms in Oklahoma.
30-06, 375 H&H and 470 NE seems like a pretty good selection that would cover a lot of scenarios.