What exercises or activities do you practice while you try to gain weight?

Personally, I believe that it is a bad idea for anyone sub 18 BMI, and who does not have doctor permission AND is willing to eat back what they burn should not work out. Whatever their relationship with food. Even the underweight but non-eating disordered are still underweight and stress from exercise can be harmful. In turn, cardio is counterproductive to weight gain, but when all of the above criteria are met, weights and resistance routines are okay.

In weight gain exercise should be essential only in my view, not hobby based. If you're in a competitive sport, talk to your coach/trainer and explain. It's better to take time off, focus and get fit for a sport or exercise in weight before you put yourself under the stress of competitive sport. And if it's totally no-go to get out of it, then to be prepared to eat it back and then some.

I do all sorts of exercise (I'm not technically underweight anymore though) and I just eat it all back. It's not so hard to do, and I really want to be a chef someday so I practice new recipes and cooking (and therefore, tasting) a lot.

I also don't just exercise because I feel like I have to, or to burn calories. I LOVE the way I feel and I really enjoy it. If I don't feel like doing something one day, then I don't. If you're going to do heavy exercise in recovery, you have to make sure you have the right motives.

While i want to gain, I'm limiting all my aerobics and cardio dance to just once a week which sucks because it's really fun but will be worth it in the end i'm sure.

Gym twice a week give or take for resistance training and I always eat WAAay more on these days  - think it's the muscles begging for more foods hehe

Other than that, I'm just walking around school carrying bags, normal tasks at home, walking to the shops etc.

I'm gaining weight and go to the gym 2-3 times per week. I don't do much cardio exercise and when I do, the machines count the calories burned and I replace them! I mainly go for strength training with weights and make sure I have a good protein/carb snack afterwards. This is just my personal routine, I enjoy it and I'm putting on weight steadily.

Thanks for your opinions, I value them all.