i laugh at your puny ziplock... i have a box full shot glasses from the major sports stadiums i visit
We collect "icons" (essentially the same thing as tiki statues but whatever little trinket we can find to display on this table) and refrigerator magnets.
Damn.....I forgot about my biggest collection. I have a HUGE collection of fat cells. It's sad, but I visit zagat.com, chowhound.com, and egullet.com about as much as I visit clutchfans......especially before a trip.
Bills are good and they usually tell you something more about the culture than any other souvenir. For instance in Hong Kong now since the handover they've been getting rid of all of the money that showed the Queen of England and while the money still looks the same they've replaced the Queen with some flowers. Another thing I like to get from places that I go skiing at are trail maps. At places that I visit that don't have skiing but have subways I like getting a subway map.
i like to collect things that are cheap or costs nothing at all. like in vancouver, i took back this pair of disposable chopsticks from this amazing japanese buffet restaurant. other than that, i dont really buy any souveniers. i shop at new places, but stuff that i planned on getting anyway like sunglasses, electronics, etc. nothing souvenier-ish.
I usually keep the local transit maps of the places I visit too. It's the one item, besides photos, that bring back the most memories since I'm usually looking at one often during the trip (in a discreet, non-tourist way, of course ). I also keep the free, local magazines that you can find on the street. They typically have more non-mainstream articles, but more importantly show the local concerts and events for the week in that city. I make sure to read them to get an idea of local/non-tourist places in the area.
Coffee mugs. Most of the stuff you pick up is either junk (key chains, etc) or you only see once in awhile (x-mas ornaments). Every morning I get my cup o' joe and get reminded of a cool place I visited. They are also inexpensive and you can get them at almost any destination.