No rig experience, but a 9 year veteran of physical, hazardous work (tree climbing/maintenance/removal) so I there may be some carry over, fwiw.
You probably won’t find you’ll need to perform any herculean feats of strength or endurance in the standard athletic sense. You will however need to find/develop the mental toughness to keep hustling when you’re sore, cold, wet and dog tired. Physical adaptations will follow if you keep your food and sleep somewhat reasonable. On that note, stay away from hookers and blow (or crank, or excess booze or whatever else). Serious. If you really feel like you need to “train” in advance, I expect deadlifts, odd object lifts and farmer’s walk variations would be a good bet.
On hustling: be Charlie-f’ing-Hustle, but find that sweet spot where you’re not a hazard or others to yourself and you don’t get underfoot. This can be tricky to start with. Don’t screw the pooch, but don’t be afraid to take a second to slow down, look around and figure out what’s going on and where things could go sideways.
Keep your head on a swivel, listen to and watch the old hands, keep your mouth shut for the first little while unless it’s to ask pertinent questions, and learn to shrug off verbal abuse, ball-busting and practical jokes of all kinds. Do not bitch, no matter how miserable you are. Embrace the suck. Think for yourself and use common sense, but realize you don’t know anything.
Invest in some decent, well-fitting boots (I like Vibergs and Danners), long underwear and whatever condition specific clothing is appropriate. Do not cheap out on this, especially the boots. Also, I highly recommend breaking the boots in pretty thoroughly before you start work, if at all possible. Always carry a sturdy, sharp single hand opening or fixed-blade knife. Nothing flashy or “tactical”-looking.
Be safe, stay out of debt and bank no less than 10% off your take home, no matter what. All the best.