If I could suggest anything, it would be to get a physical NOW, especially since you are transitioning back to a more physical job. By your own admission, you are out of shape and have been smoking, and I would hate to see anything happen to you. Start slow, especially at work. Keep hydrated, keep yourself as cool as possible when the hot weather hits. If you get tired, REST. It will be hard. Your ego won't want you to do it (and probably your boss either :D ), but you do not want to get a visit from the boys on the ambulance. I am not a doctor, I don't even play one on TV, so please take all this with a grain of salt, and contact a professional if you are really interested in getting into shape. Afterall, we're just strangers on an internet board, who are we to suggest anything :D .
As for working out, especially if you are traveling a good bit, check out some body weight exercises instead of a home gym, at least to start. Walking is great exercise, you will be surprised how much good getting at least 30 minutes of walking a day will do for you. If you are wanting to get ready for a big hunt, you can work your way up to walking with a weighted backpack, just be careful. Again, please start slow, ease back into it. An injury will only delay things.
We have a workout we do, and all it takes is a deck of playing cards. It's also something you do with body weight and can do easily in a hotel room (get a ground floor room :D ). You assign each suit an exercise (or each color if you really want to challenge yourself, so that you do only 2 kinds of exercises instead of 4).
So let's say that hearts are squats, diamonds are pushups, spades are crunches, and clubs are forward lunges. You shuffle the cards, keep them stacked face down. Flip over the top card. Whatever that card is, the suit dictates the exercise, and the number on the card is how many you perform (face cards are 10, aces are 11), so if it is an 8 of diamonds, you do 8 pushups. Wait until you are standing again to flip the next card. Repeat until they are gone. I hope that makes sense, if not let me know.
When you start, maybe draw 13 cards at random and only do them. Build up to doing the whole deck. It is a challenge, and alot harder than it sounds!
Another exercise to consider is the good ole Burpee. I figure if inmates can stay in shape using them, it should work for a guy in a hotel :D Actually, I stole that idea from Mike Rowe of Dirty Jobs haha.
Anyhow, keep us posted on how it is going, and remember, I'm no expert and I can't promise that nothing bad will happen if you try what I said (CYA at it's best
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Good luck!