Pallette was the case that held the ink cakes and reed pens, and where they mixed water on the ink cakes to write with the resultant ink. They wrote on papyrus, unless they were learning then they used either clay tablets surrounded by wood, or I think wax tablets the same.
As for what they leaned on, I believe most used low tables where they worked rather than carried what we'd call a lap table with them. At least I have seen no references to any portable leaning surface for writing on.
Ah, found an excellent rewference for you. http://www.eternalegypt.org/EternalEgyptWebsiteWeb/HomeServlet?ee_website_action_key=action.display.module&story_id=37&language_id=1&module_id=242&ee_messages=0001.flashrequired.text
The equipment of the scribe who writes hieroglyphs consists of a rectangular case of pigment and reeds, a pot of water for wetting the pigment, and the reeds themselves.
The rectangular case was called a palette. Most palettes were rectangular pieces of wood of about 20 to 43 centimeters long by 5 to 8 centimeters wide and 1.5 centimeters or deep.
Small circular cavities held the pigment at one end and many examples of palettes have a long central hole for the reeds, which are usually 15 to 25 centimeters long. The scribe cut and bruised one end of the reed to maximize absorption of the pigment. To write, he moistened the cut end with water and brushed it over the pigment.
Reeds with split ends, which produced a finer line, gave hieroglyphs and hieratic script an awkward, crabbed appearance. These were used in Egypt after the third century BC.
Wooden boards, which could be wiped clean and reused, also provided a good surface for accounts and calculations as well as for literary texts.
Ancient Egyptian papyrus was cut from the stem of the plant Cyperus papyrus into strips that were never more than 50 centimeters long. Strips were laid out side by side and a second layer was placed over them. The two layers were beaten together and the natural juices in the plant provided enough adhesive material to bind the fibers together. The resulting sheet had a smooth light-colored writing surface. Individual sheets, about 48 centimeters by 43 centimeters at full size, could be joined together to create long rolls.
The oldest roll was found in the tomb of the First Dynasty Hemke at Saqqara. The roll remained the natural form for books until the Roman period when it was replaced by the codex, a set of individual sheets bound together in the manner of a modern book.
So, yes, you're right, wooden wipe clean boards were used like the ostraca for temporary work and figuring.
Some nice pix -
A famous image of a scribe writing.http://openlearn.open.ac.uk/file.php/2484/MA209_1a_003i.jpg
A modern replicxa of a scribe's kit.http://www.kingtutshop.com/WritingKit/writingkit.htm?gclid=COa64qWUg5sCFQ0MDQodkBGsdA