I think this would be a good idea. Not sure how much money you would make though. Small quantities of items are often not available, such as large trash bags, small ziplocks etc. It is maddening to pay a $6.95 shipping charge when the actual postage is $0.75 and in a regular envelope (less than $0.10). Many of the small things are easily mailed by first class mail for a reasonable cost.

I would look at what items you would want, put a price that you think is reasonable and then check out how much it would be to mail it including envelopes, postage and other related charges. You need to find a balance between what people will pay vs what it will cost you to provide the items.

I agree about the cost of shipping built into the item's cost. It is not nice to find a great price on something and then get blown away by the shipping cost. You could also have separate prices for larger quantities that would perhaps have a separate shipping cost if it made sense.

You may want to take some items to the post office and weigh them to determine what they will cost to mail them.

Good Luck!