Here is a very cheap, very convenient, way to paint at the top of a ladder without having to hold both a brush and a paint bucket. It can be installed on a ladder in 2 minutes and uses a removable disposable beer cup to store the paint. This allows you to refill or replace the paint without having to take down the ladder. It is also cheap and disposable so that you don't have to clean anything when you are done.
Step 1: Clamps
First buy two clamps, one should be big enough that you can fit it around a plastic beer cup, and the other should be smaller and will fit around the horozontal rung of your ladder (with a cloth or towel wrapped around it).
Step 2: The Way the Clamps Are Fitted Together
Fit the clamps together as shown in the image so that the cup holder will work properly.
Step 3: Install on the Ladder
The image shows the way it is installed on the ladder. The cup easily comes out when you need to and it does not fall out when up on the ladder.
I have found this set up very convenient for painting trim or touching up the side of my house.