They shared with me that the best way to do this was to actually wait until the plane landed and then go to an ATM with my bank card and withdraw currency. This works especially well for me because my bank has agreements with almost every ATM company and reimburses fees associated with using an ATM. My bank offered the most favorable exchange rate for local currency using the ATM method.
Also, the 10 and 20 cent coins are very close in size. This will be important to know when you're trying to read the coins without glasses to give the nice lady guarding the public bathroom door her 40 cents. Not to worry, should you get it wrong she will chase you down to let you know. For what it's worth these bathrooms are always tidy and well stocked with toilet paper and soap, in my experience, so it's worth the 40 cents.
It also merits understanding how your credit card converts the price of purchases you charge. My last trip I did not have a strong grasp of this (in addition to my weak mental money conversion skills) and ended up paying more fees for using my credit card and higher exchange rates than I expected. This trip I purposely used a credit card that had no fees for currency exchange. Occasionally you will be asked if you prefer your charges in Euros or Dollars. Always choose the local currency; using the offer to convert to dollars has additional fees attached that may be hidden.
As for converting prices mentally when making purchases, it is a moving target. Generally speaking it seemed that if I added about 30% to the price I was in the general vicinity of an item's cost in dollars. After a while I just started thinking in Euros and thus fooled myself into believing things were less expensive than they were. Fortunately I'm a deep discount shopper anyway so this didn't hurt me, but if you are a shop-a-holic at home there are a ton of apps you can download on your phone to help do the conversion and most store clerks are helpful as well.
Please comment with your conversion tips as they may be the most helpful thing to know when traveling abroad.