You will unlock energy drinks as you gain experience for playing, which will increase your Street Rank. When you hit certain levels in Street Rank, you will unlock more energy drinks. You use energy drinks by going into your inventory between matches, or while looking at your Street Rank on the main menu with the right thumb stick. When you do this, you will need to hold the A button to use the wanted energy drink. When it is in use, you will see the countdown timer on the left of the screen above the used drink. You should just need to do it five times, but it is slightly buggy right now. I had to use 6 before it unlocked for me.