I am not sure why the backpack isn't more popular. Out of any possible means of holding items, backpacks make the most sense by far. Even weight distribution, hands free, organization, so much room for fun activites... the list goes on. The fanny version of the pack is also another good option that seems to come in and out of style (I will spot a Louis fanny on occasion).
Although none of these top by speaker backpack, they come close... and are definitely more stylish.