J.K.
i didn't buy a gift for my children when they had siblings born. They maybe got a little something from grandma or aunt at baby shower because they were there ofcourse but nothing from mom and dad. Although maybe we got a new coloring book or some toy to take the day of delivery since being stuck in a hospital room after mommy has a baby isn't all that fun- but maybe we didn't and just brought a favorite from home- i really don't remember. Yes the baby will be getting stuff and attention but buying your child some new thing isn't going to stop them from feeling left out. Involving them, giving them just as much attention as before (yes it is possible) and not leaving them out is what will keep them from feeling left out.
By the way- my youngest was born on my daughters 2 birthday.... that was all the present she needed.
Hope this helps :)