Hello,
Since you are asking which supplement to take in order to bulk up instead of asking how to bulk up, it means you already know the basis of bulking. So instead of asking you to eat more calories than your RMR, let us take a look at the difference of the supplements and the pros and cons of each supplement.
Weight/Muscle GainerThe name spells out everything. BUT don't be fooled by the name. If you take a look at the nutritional facts, they are just protein pack with either more fats or carb or even both. It is usually costly and hence, not worth the money. You should only take weight or muscle gainer if you found out that you are not able to get sufficient calories for growth. If you were really keen to take weight or muscle gainer, I suggest you to make your own. There are hundreds of free recipe out there with different ratio of carb, protein and fats and here is one for you - blend 2 scoops of whey, 500ml of skim milk, 2 tbsp of natural peanut butter, 1/3 cup of oatmeal. Of course you can add in other ingredients like banana or even flax seed to boost your very own homemade weight gainer.
Protein PowderProtein powder is the most basic supplement for all lifters. There are many kind of protein powders like whey and casein to name a few. Whey is normally taken as a post workout drink as they are digested easily to supply your muscles with essential amino acids for growth and repair. Casein is normally taken before you sleep to supply protein to your muscles while you sleep as casein takes longer to digest. Protein powder can also be taken as an alternative to your daily protein intake as they are easily prepared. They are versatile and can be added into oatmeal and be made into homemade protein bar. Hence, I will suggest protein powder.
CreatineCreatine is probably the second most popular supplement after protein powder. It is taken to replenish your ATP which is like a fuel for your muscle. It will also retain water in your muscle so that your muscle will have sufficient water for metabolic activities. It will normally result in water retention which may make your muscle look bigger. Creatine is completely safe and many athletes around the world are taking them to boost their performance. I will only suggest you to take creatine only if you hit the gym regularly or wants to improve your performance quicker.
Well, these are the breakdown of the supplements. They are just for your information and should not be your only decision-making factor. (In case you regretted your purchase and blame me!

) You can search the web to research a bit more before you make your purchase. Of course the best way is still to eat more than your daily RMR!