You could try to fill once it is cool. Never in a hot engine. And see where the leak is. It could have just been a low coolant turns to steam and blows all out through the relief cap event. If you are lucky.

Fill. Start engine with cap off.
Watch water flow with cap off.
If all is ok after a few minutes, put cap on.
Let idle until operations temperature.
Leak? Then take to shop.
No leak and hot. Continue trip. carry water in jugs.

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2005 X5 4.4i SterlingGrau, Sport Package, DSP
Build 3/12/2005