I currently organize my shells by chronologically by trip.  Most of
them are stored in ... plastic containers with transparent covers - the
kind you get airline snacks, fast food salads and sandwiches, supermarket
baked goods, and catered box meals in, and several containers previously
 housing radio head sets - these have indendations that often fit a
particular shell perfectly and show it beautifully with the backing
providing stability.  With beautiful shells inside, often on cotton,
one can't even notice the "US AIR", and "Wendy's" imprinted in the cover.
of some.Paper labels can be soaked off.  These come in an array of
sizes and shapes and are
great for medium size shells,
for a number of a particular species found on a trip, and for combinations
of several species.  It's great when I find a bonanza, i.e. last weekend
I attended a huge catered picnic lunch. There were various containers
as described. I just mentioned that I wanted to save these as specimen
boxes for my shell collection and people passed them right too me with
nary a funny look.A quick soapy rinse and drying and they were ready
to receive specimens.  As I said, they are great for showing the shells
and also they stack well so if I need to move some things along to
make room for new acquisitions, I just pack them in larger cardboard
boxes,by trip, label them and put them away.  And the containers
don't cost a cent.

Really small shells go in specimen boxes, 1"x1"
and 3x2", and  baggies in an array of collectors' sizes, that I get from a
dealer.

Karen