That's an interesting problem! Here are some ideas:
-- Carry the USB stick around in your pocket for months and hope to remember to give it to your friend next time you see him.
-- Make a date to see your friend. Then you can use your tickle file.
-- Think up a reason to see your friend -- for example, buy tickets to a concert and invite your friend to the concert. Maybe your friend's birthday is coming up soon or something. Take the opportunity to do something that's good for your relationship.
-- Put it on the agenda for your friend, but within parentheses so it's easy to ignore when you're on the phone. However, try not to get in the habit of automatically always ignoring it.
-- Try to predict where you'll be when you see your friend. Put it in a "special bag I bring when I'm going to restaurants" or something.
-- Try to predict when you'll see your friend, or make a decision that near a certain date you'll invite the friend to meet. Then you can use the tickle file.
-- Try to predict how far ahead of time you'll know you're planning to get together
with your friend. Then you know how often you need to be reminded about the stick,
and can use the tickle file and, for example, keep re-tickling it 10 days into the future.
-- Collect it together with other "things to return to people", possibly also using the same collection for gifts you buy for various people.
-- Make a set of checklists: "things to bring places". For example, it might say "swimming: bathing suit, towel, lock, leave wallet at home but bring entrance fee."
When you review your calendar, or before leaving home, you can review the
checklists for the activities for that day. The set can include a checklist for seeing
your friend. You might add one or two more items to make it easier to remember
to look at the checklist at all; perhaps cut out a cartoon or article you can give
to your friend, or write "Seeing Bob: agenda, pencil, USB stick."
-- (Use your memory for this one thing. Hmm, not really GTD, though.)
-- (Ask your friend to remind you. Not really GTD either.)
-- Maybe somebody will invent a device that will beep when your GPS position is close to your friends'. And then one that will predict, before you leave home, that that's going to happen that day ...
-- Maybe somebody will invent software so that when you enter your friends' name into a calendar entry, a reminder will pop up. Possibly you're already using software that could be configured to do this. When you see the reminder you can then put it into the tickle file or an alarm to go off that morning or something.
-- Turn the USB stick into a piece of art, sell it, and send the money to your friend electronically. (Just kidding.)
-- Start a GTD forum thread about it. This will raise the salience in your mind for that one item, so then you'll probably automatically remember.
Inability is an abstract thing involving comparison with alternate universes; it cannot be experienced.