I weigh the same as you and find that I need the ATRS to effectively right my boat.
ATRS-Alabama Trash Righting System
(not too much or it will burst
Hey now let's save those trash bags for the trash.. <img src="http://www.catsailor.com/forums/images/graemlins/cool.gif" alt="" />
For heavier platforms Wet/dry bags work well (to a point). They are mass produced so relatively inexpensive, won't burst and make a mess, and can be easily clipped into the righting line. Wet bags come in various sizes. One liter water weighs roughly one kg. i.e one liter water = 1 kg.