Envelopes are the real problem with anything smaller than the Expression. Envelopes are cut on one sheet of paper and are folded almost in fourths when assembling. With a 6 inch maximum, the largest envelope you can make is 3-4 inches. You'll have similar problems with bags & boxes.
Think about how the bags & boxes are folded/created and you'll see why the larger format is necessary -- unless all you want to makea are little table favors or something.
The gals on the Cricut discussion boards are really helpful when it come to questions about what can/can't be done with the various machines & carts.
Board home page:
http://www.cricut.com/messageboard/
Here's the link for the Tags, Bags, Boxes and More board:
http://www.cricut.com/messageboard/tt.aspx?forumid=35
The Wild Card board has more info about envelope issues:
http://www.cricut.com/messageboard/tt.aspx?forumid=107