I always do grocery shopping on the bike.
A backpack can carry lots of stuff.
I've had 1 gallon of milk + bag o' bagels + head of lettuce + bananas + more in my backpack.
Only had 1 problem -- one nite someone stole DH's seat off his bike while we were in the store for just a coupla minutes. He rode home with no seat (coupla miles)!
And a few times I had to sling a bag over my neck to carry extra stuff that wouldn't fit in the backpack.
And some times I have to stuff a bag up under my jersey (but that's usually a taco bell bag).
laurie
Brand New Orbea Diva | Pink | Specialized Ruby
2005 Trek Madone Road | Pink | Ruby
1998 Trek 5200 Road | Blue | Specialized Jett
???? Litespeed Catalyst Road | Silver | Terry Firefly