Rule to determine headings in the circuit
The digits of the heading for each leg (crosswind, downwind, base and final) all add up to same number. For example if runway 35 is in use (3+5=8), then crosswind heading (080) downwind (170), base leg (260) and of course final (350) all add up to eight. Now try it for any other rundway! (Okay, if you picked a 290 heading, you will have to add the digits of the '11' you get from 2+9 once again and make 1+1=2, because the otherheadings (020, 110 and 200) all add up to 2).
Another good rule of thumb :-
Kilograms to pounds rule is simply to double kilos and 10% (This accurate to within five pounds in a ton).
Both these were in an article in the Pilot magazine about a year and a half ago, if you can dig out a copy there were about 16 really useful 'Rules of Thumb'. It would be worth typing out the ones you would use most and getting a copy laminated to keep in the cockpit!!
Good luck!