tri x, or delta 3200 and a monopod... Also makes for walking stick and defensive weapon, and can shoot down to 1/8 or so when you use camera strap and the existing bi-pod you take everywhere with you.
Bracing against light poles or walls, etc. Second body is nice, but I would rather note frame, rewind, mark film leader with sharpie, then if I only had a few - to half of the exposures used, you can reload, shoot blanks with lens cap on till you get to the previous last frame, advance 2 - 3 more and go on your way.
Another trick, if you just need a bit more speed, and are not way off - velvia 50 loaded, and B&W 1600 needed... is to just shoot 4 blank frames ( 6 inches of film ), and then shoot the same film and plan on pushing it. Make note of the frame you were one before you started with the underexposed stuff. Back home, rewind till the leader just pops off. Reload and advance to the noted frame. Advance 2 more. open back. place finger gently on film at the take up side of the shutter. Crease film strongly there. ( or cut and place in light tight film can or load and process ) Rewind and note.
Later when processing, cut the film at the crease, and process the original end at the normal dev, and push the tail end. You can also do similar with 120, but it is a pain in the arse. Just give yourself a blank frame or two. For me, if I am mostly done, I just call it good and rewind & reload ( obviously no rewind on 120) . If I have just started a 24 or 36 exp. roll, I advance a few and shoot, later do the crease or process. 120, really depends on where I am in the roll. Easy enough to rewind it on the spool in the darkroom, retape at beginning, wind back to the blank frame, and cut and develop. Just thread the tail end in the reel, as the cut end usually is a bit short to avoid damage with the clip. So tape end gets threaded - and tail end gets threaded, and the cut frame is usually fine.