The most commonly forgotten item that I seem to observe...
Common Sense.
On a day to day basis, I encounter a lot of different people. And for the most part, all these folks are extremely intelligent people. But yet, simple things can baffle them.
The biggest thing... If you read the signs, 97% of the time, they will answer your question before you even ask it. But unfortunetly, with the Common Sense forgotten at home, just laying on the kitchen counter... folks wont read that sign.
For example... I'll pull into we'll say the Swan... I'll be driving one of the new Nova low floor busses, with the giant amber LED destination sign. You can read these things from a mile away. Anyways, I'll pull into the Swan at night with "MAGIC KINGDOM" on the sign. 75% of the time, someone will come up to me... "Do you go to Downtown Disney?" Sometimes people will just jump right onto the bus, without asking, and then wonder why the bus is headed in the "wrong" direction.
My favorite though... my friend pulled up into the Magic Kingdom load zone at one of the All Stars. This guy and his wife walk up to the bus. The guy looks at the sign at the bus stop... then looks at the front destination sign on the bus. He thinks for a minute, then looks at the signs again. He then gets on the bus, and asks, "Do you go to the Magic Kingdom?" The wife at this point takes her purse, smacks him, and says, "You saw the sign at the bus stop, you saw the sign on the bus, you KNOW the bus goes there, now why are you asking him? Go sit down!" My poor friend had to bite his lip to keep from laughing.