How do I drop multiple items?

Solution 1:

There is actually no way to drop multiple items, but you shouldn't be just dropping them anyway -- share them with other users!

Solution 2:

At the time when this question was asked there wasn't a practical way to drop multiple items at once. Now we have the capsules which we can use to drop multiple items at once.

You select a capsule from your items (preferably an empty one), press the "Load" button on the capsule actions screen, select the item(s) from your inventory (which is unfortunately listed alphabetically), select the number of items to transfer with the arrows on the upper side of each item and press the "Transfer" button at the bottom.

This way you fill a capsule with the items you want to drop. The downside of this action is that you have to drop this capsule on the ground loosing the capsule and giving your opponents an opportunity to find a treasure chest. So the capsules are more effective if you are passing your excessive items to another teammate.

Solution 3:

In a hangout the Niantic devs said that bulk actions are on their todo list. But they are a small team, so it probably won't be soon.