oh god. no offense your friends are the brightest of the bunch!
food NO WAY! solids are ment from 6 months +, and even before the age of 1, solids are just for fun and learning about texture and chewing and swallowing. your baby needs calories and nutrients, and those are in baby formula or breast milk, its the MOST important thing your baby needs right now.
door bouncers/jumperoos/walkers. wait till later on. your baby needs VERY good head control to use a bouncer or you can injure your babys neck and spine. my LO went into a jumperoo at about 4 months old. he had good head control before then but i waited till he had VERY good control as its not a risk i wanted to take.
none of this means your friends babies are more advanced then your LO, it just means that they are potentially making mistakes because they either dont know the information or they dont care about it or their photos are in the wrong albums!
edit to add: my LO didnt sit up till past 6 month of age