Maybe the Snap-On dealer would kindly trade your standard wrenches for metric? If they are brand new he should have no problem reselling them.

I know you said you were thinking of using them for travel, but consider that if you are broken down beside the road, the last thing you need is tools that "don't quite fit". You run the risk of rounding off fastener heads and being unable to get the car going.

I would suggest that you consider buying a set of craftsman metric tools to throw in the trunk, I know they are not anywhere near Snap-On quality, but they are inexpensive and usually adequate for anything you can do beside the road.