You have gotten some interesting answers of which I dont agree with all of them. First off, it is a lot more economical to buy a 50lb# bag of feed than a 5,10,15,20, or 30. I would find a reputibale feed supply source. Maybe a co-op or tractors supply as an example. A metal garbage can is a good place to store it without mice, squirels and the like. It also shouldnt mold or clump from moisture if stored inside a garage or storage shed before you use it all.
Now, lets talk about your food! Starter poultry food is generally used until birds are about 3 months old. I assume you have hens or pullets for egg laying? (Meat birds feed is a little different but not much). Changing feed at different ages is a step by step process controlled by age mostly. Most purchased products have a chart on the back of the bag to tell you when to change to "their" next product line. It is a good reference, but not all products have the same ingredients. Kind of like buying dog or cat food! One has meat byproducts and another is chicken and rice! This is where you need to get some feedback from people and also the "chickens". How well you chickens eat their food is most important. If they turn their nose up at it so to speak, try something else. Example: I ran out of a high protein mix and purchased a supplemental bag at a feed store until I could make a run to my regular store whithin the week. They ate it sparingly but werent happy with it.
At 3 months you are ready for the next update in chicken feed! Questions to ask: High protein, low or moderate protein, calcium, medicated or not, oyster shells, grit,and more come to mind just to name these. Points of interest that I have been told by my supplier and bird raiser. DONT give birds high levels of calcium, oyster shells or other egg shell developers at this time. It can cause kidney failure and some respiratory problems in birds of a young age and not fully developed yet. If you want your birds to beef up as a meat bird I suggest the high protein of over 20 percent. If not 20% or less is fine thru this stage. Grit or gravel is also okay to start using now. It will help them to digest their food. Calcium and oyster shells come in the next stage of feeding maybe or maybe not depending on the ingredients in the product you buy or the breed or weight of your birds. You may not need it. I hope this may help you a bit. Good luck!