I've been collecting pressed pennies from our vacations elsewhere for years. I'm really looking forward to getting pennies from WDW on our vacation.
Many people wonder why they should even bother with cleaning them. Aside from the obvious - i.e. they look better - dirty pennies will not press as clear. They will also gum up the die and make maintenance requirements more frequent. The reason so many presses are out of service so often is for that very reason.
I've tried ketchup, lemon, vinegar, brasso and all the rest. Hands down, the very very very best cleaner is the copper paste polish used for cleaning copper pans. But forget the sponge, use your fingers to rub it or an old toothbrush. It can be found in most grocery stores or in department stores.
A bit of advice - a lot of people just use new pennies and they do work well, but many times there will be a streak in the finished piece. New pennies are zinc with a copper coating. The streak is the zinc showing through. To avoid it, only use pre 1982 pennies. Also - be sure they are completely dry or they will turn green fairly quickly after cleaning.
We went through my daughter's penny bank and in 10 minutes had 2.00 worth of older pennies. A quick sort through them to remove the really grungy and pitted ones netted us about 120 suitable pennies. It took about an hour to shine them all up. We put them in M&M minies tubes - 2 quarters 1 penny at a time. Now we're set - just pop out the tube, slide out the penny and its accompanying quarters and finished.
Also - we use the empty 35 mm film "barrels" to store our pressed pieces in until we can get back to the room or home. Nothing gets lost and we don't have to carry the book with us. You can also use old prescription bottles to hold them.
I hope this helps.