The toughness of true rangefinder cameras will be limited by the very focusing system from which they get their name.
The toughest is probably the old Contax II rangefinder. Even better would probably be a Kiev 4, since the rangefinder design used in those cameras was probably a little more resistant to damage from small dings and or drops. Maybe not 4 foot drops but the Contax II (the predecessor of the Kiev) was regularly used by photojournalists back in their hey day. Kiev 4 cameras are a Russian version of the Contax and they are far cheaper to buy in usable condition.
I have used a number of the old metal, mechanical slr cameras that could absorb quite a bit of punishment, but when traveling, hiking, skiing or boating it may make just as much sense to just pack an inexpensive camera that can easily be replaced if they succumb to the abuse.
I currently use the GA645i for hiking because I prefer the 6x4.5 negative to 35mm. I know it has worked quite well in hiking situatioins including cold weather (keep the batteries warm), snow, rain, dust/dirt, etc. It is fixed lens and it works in a similar fashion to a rangefinder. I have not yet taken it to the beach so I'm not too sure how well it would work in that environment. It is also not as inexpensive to replace as the older metal slr cameras or the Kiev would be.