<Snipped quote by Paradigm Shift>
Dude!!! If you find out how to put on weight TELL ME!!!!
I'm not joking that I eat non stop and eat pure trash and sugar, and I am still less than 65kg.
You need protein mostly. I regularly work out with weights and use a lean protein to stop the fat but keep the muscle. I have to use Soy Protein because I'm lactose intolerant but to be honest it's a better source and a healthier one. Putting on weight without having to buy a new wardrobe is a tough one but eating junk won't do much other than give you an early coronary and make you depressed. Your waistline will increase fast while your mood will plummet. That's why America has issues.
Eggs, natural peanut butter, soy milk, red meat, spinach and other dark greens... eat the good stuff, workout and you'll balance yourself out.