I swear, anyone this low on clues needs to be on auto-reorder:
Today, my slush pile coughs up a true cluefree querier who managed to send his query letter and pages postage due. And not cause he missed it by half an ounce. He stuck ONE first class stamp on an envelope with five pages and an SASE. THAT is clue free.
When you start the query process you don't have to weigh every single envelope but you should weigh ONE to get an idea. And if you don't have a postage scale, your local supermarket does. They keep it in the deli department. The post office will even tell you the amount of postage to put on various weights via their website.
As for clues, well, I keep mine in a jar by the door just to make sure I never leave home without one.