Consider the number of birds you are going to keep and then pick up the supplies accordingly. For example, before buying a cage keep in mind the number of birds you are going to accommodate.
Consider size of birds before buying supplies, especially cages. A bigger bird will need a bigger cage, more food and will need more grooming stuff. It requires more effort to manage a bigger bird.
Be assured that the material used in making the supplies for example cages is safe for your birds. A cage made of sharp steel wires can pose injury risk.
Make sure you have got vaccinated your birds before buying other supplies. It will protect many viruses and diseases. Also, get vaccinated them against seasonal or weather risks.
Pick right feed for the birds. Specifically mention about the bird for which you are going to buy the feed at the shop counter, and read instructions carefully before feeding them.
Choose purpose-made feeding supplies for them. For example, buy a purpose-made feeding pot. This will make it convenient for your birds to feed themselves.
To protect your birds from harsh weather conditions buy a cover for the cage, especially if you do not want to take the bird inside home because of bad smell or for other reasons.
You will also need to buy some grooming stuff, for example, nail cutter, for your birds. You might need to clean your birds regularly and manage their skin or hair needs.
Also buy some stuff for your birds to play with. This provides them an opportunity for exercise and keeps them healthy. It will also make you feel good and entertaining when your birds are playing.