Because I don't know you it can be hard to make recommendations but pretty much all of the above will work for most. You have to want to do it and you have to make the changes that will stick so you can maintain whatever it is you want.
Life happened to me to and the move to a desk at work along blah, blah, blah... my fault, here I am. I started doing all of the above (posts) and more. Some stuff worked, some didn’t. You have to find what works for you. Be careful and don't tear up your knees/ancles/hips... but get after it. I can heartily recommend:
Definitely get the myfitnesspal app and log EVERYTHING you eat and drink. You can put it inot social media for all to see, critic, cheer, laugh - or keep it to yourself. You can also log exercise/activities and have it auto sync with a tracker.
Get a tracker (Garmin, Fitbit, etc). Log the stuff you do not just daily steps. It will help you see what it working well and what isn't as much.
Walking, a lot. Start with short walks and work up to distance with your ability. When you get a few miles, amp it up and walk faster, make sure to include hills, big steep hill, make it harder and get the HR up. Worry about the pack later.
Get a bike and ride. Search Craigslist, newspaper, maybe even arfcom for a solid used bike and move up when/if you think it will stick. Who gives a shit what brand/model/style - see if this is something you will get into then geek out.
Gyms are full of stuff other than weight. While strength conditioning is a good thing there are tons of cardio options from all the classes (laugh but those jump around and dance and stretch classes will bust your ass!) to spin to just a stairmaster, treadmill, row machines, eliptical....
Running. Burns a lot of cals fast and I am breaking that "plateau" by running. Slow, but getting it done.
See if you can find a group or a couple folks on your hometown forum. Maybe check in with the local run/bike/hike shop or local web based groups?
This may be the most important thing really - you can't out run/walk/work out poor nutrition. Eat real food. No more junk, crap, fast, enriched, bullshit foods... Health is more about nutrition than exercise. Occasional pizza/beer night
One of my rules is - you can quit when your underwear is soaked with sweat... Working for me, good luck!