No Canadian pennies please... they jam the machines and then nobody gets pressed pennies.
I haven't used two-way radios, I have heard that there are too many other families using them, but somehow I don't think this is really the case anymore because just about everyone uses cell phones now, I don't think I've even seen anyone with a radio in at least a year or two in the parks - you could give it a try... I would say that it would be really annoying though if you get called while on a ride because they are pretty noisy and might ruin the experience for others on the ride. Whether you use them or not, make sure to set a meeting place where you know you can meet up at certain times of day (or when you can't find one another) so that you at least have a backup plan.
from what i gathered, 2 way radios work great since everyone else thinks a lot of people use them. Then main thing about it is that your outdoor, its hard to hear someone talking on it... need to find a way to beep the crap out of your other party... Same thing happens with Cell Phones...
just dont get too high tech though... Disneyland has a huuuuuge radio network.
I disagree with the canadian penny previous post, I have seen and used many canadian pennies and I think they turn out better. Canadian pennies are usually shinier and so they look much much nicer. Never had or seen a canadian penny get jammed.