Here the list over things you need to gain weight

As you might know, protein powder is the absolute best thing to use when you are trying to gain weight trough the training on the gym. But there is also other products that you can use to gain weight. Protein powder is of course number 1, but here is the complete list:

protein powder:
provide essential amino acids and has other health benefits
Used from 20-300g per day depending on body weight ..

Essential fatty acids (DHA & EPA)
provides essential fatty acids for those on low fat diet.
5-30g per day divided in several doses

better health, gastro-intestinal control, better cholesterol levels, better imunsystem ..
used 10-30g per day from food and / possibly grants

Flaxseed Oil:
better health, excellent source of important Omega 3 fatty acids
2 tablespoons per day or more if desired

Gamma linolic acid (GLA):
good for skin and hair, reduces joint pain
400-600 mg per day

Glucosamine:
effectively reduces joint pain, helps in tissue damage
500-3000mg per day