I always get a stuffy nose on planes so have a small pot of Vicks in my bag, as well as lip balm, moisturiser, wet wipes (that I've had in the freezer so nice and cold), a roll on aromatherapy wrist thingy, deodorant, boiled sweets, chewing gum, chewy sweets, cut up apples, cut up cucumber, carrots, baby tomatoes, chunks of cheese (sometimes), crisps/popcorn.
Then.. phone charger, audio books, clean undies, couple of pens, notebook, peppermint / green tea bags, windeze (?) Tablets.
Doha airport is very big which isn't a bad thing as it'll give you a chance to stretch your legs. You'll have to go through security as you transfer which is a pain and they have been know to take water away.
Realistically on a 4 hour transfer, you'll only have about 2.5 hours to kill.
Oh, one last thing.... it may be a bus job from where the plane parks to the terminal so you get a free tour of Doha airport (10-20 mins) 🤣