Buying good quality protein like cheese or a barbecued chicken would be an easy way to boost your calories. Avocadoes are easy as well. I love avocado mixed with a hard-boiled egg & a little low-fat mayo, salt & pepper. I also add a little of our home-made rhubarb chutney for flavour, but it isn't necessary. It's simple & very handy as either a snack or a meal. Do you like bananas? Great as a filling & nutritious snack. Dried fruit? Hommus?
You are doing well with your exercise. It's good to be able to do more & more. Enjoy your achievements! Cheers, Cate