Charitable giving and wills

One of the quite unintended concerns of now being in the "golden years" is that people who have been part of your life start dying. In my parents family this started about five years ago with the death of a younger brother from cancer. Since then both parents, an older brother, and a nephew have all passed away. After dealing with the grief we (those of us left in the family) have had to learn about the legal process of disposing of the assets of those who have died. I have even had to think about the idea that I too will die some day.
One of the things that I have learned from being an executor of a will is that the government is almost always going to be a beneficiary of the estate. We think that we have an estate worth X dollars and we naturally want our beneficiaries to have this money. But we forget about the governments share. Just think about it. Many people (including myself) have RRSPs set aside for our retirement. The thing is, you have not paid taxes on that money and the government is going to get its taxes eventually, even if that happens after your death. Many people also have stock and mutual fund portfolios or rental property. These to are subject to capital gains taxes (even if at a lower rate than the RRSPs). So, unless you hold only cash and only own the real estate you live in the government is going to be a beneficiary of your estate.
Now I would rather (even when I'm dead) send money anywhere other than to the government. This is why I am thinking that my personal will (no I have not made one yet) will include a significant gift to the charity or charities of my choice. Just like when you are alive this decreases the amount of tax you send to the government. I wish there was a simple way to know just how much should go to charity to minimize tax owing to the government. I been avoiding even thinking about wills and such (it seems so morbid) but it seems to me that including a charitable donation in the will is a sensible thing to do. Oh yeah, and I do some volunteer work for a couple of charities.