Well i know these arent the best ideas in the world but these are some things i can think of...
Gifts..
You can put some peanuts in them..and decorate the bottles with ribbon or decupage(sp?)
Also could put jelly beans in them and decorate them..
Bath salts
buble bath..
or you could put flowers or herbs in oil in them!
marbles etc...
decorative bottles with small gifts in them are always a nice gift! (i wish i could get something like these as gifts..but unfortunatley i am the only creative person in my family...and my friends arent creative either LOL..all the crafts are left to me!!..not that i mind doing them

)