If I was going to be stuck with only a single shot 30/30 and having been given notice and the time to get the gun (build the gun) and get the desired supplies, I would have three bullet molds. A .310 round ball, a 160 to 180 grain reduced diameter for paper patched bullets, and a silmilar weight mold for greased bullets. I'd carry about 8 pounds of lead if mobile, or if camped or based I'd have 100 pounds. Two pounds of Black powder, five pounds of 3031. Skinner or Lomak sights, screw mounted and silver soldered in place.
Now the gun, any way I want it right? Ok I'd start with a falling block action, put fairly straight stock on it, fit it like a shotgun stock, with a wide slightly curved shoulder pad, wooden foreend glass bedded, to a .890" tapered barrel about 24" long, chamber set up as an AI with what I call dual head space, and the chamber would be "loose match" that is about .003" swell room for the brass. Long throat, and a 1:16 twist. This should get real close to .308 Win performance with hot loads.
And light round ball loads could be used for small game. The paper patched bullets would be for long range shooting (over 500 yards) at what ever needed shootin at that range, or close in when the most thump was needed. The grease grooved bullets would be the primary projectiles for general use on Deer, elk, coyotes, and two legged solo attackers.