In Western Europe you’ll hardly find any places that accept US currency. So whatever amount you take you’ll most likely carry with your all the time and bring back home. I’ve used to carry some $50-100, so that even if both Visa and MC networks fail I could somehow get out of the airport and into the city. (Now I simply bring 50-100 Euro back to the US to have them on my next trip.)

Whenever I travel I’ll bring $200-300 with me.  I do this for a couple of reasons.  First, I keep some for my US airport layovers/food/taxi if needed.  Second, I exchange the most of it right at the start so I have some Euros from the start.  It saves a bit of money it costs to pull from an ATM.  Call me old school, but I like to have a litte hard cash on me at all times. 

I used to like to have about $200 in cash on me upon arrival.  I was mainly concerned that some ATMs wouldn’t accept my bank card.  But, I haven’t been rejected by any ATM for at least of couple of years now, so I just wait until I’ve arrived.

If your cards don’t get rejected in ATMs at home on a regular basis, you chould have nothing to worry about in Europe. 

 
I like to add  a little excitement to my travels.  I bring only an atm card from a small local credit union that doesn’t work in 99% of foreign ATMs. I try to use my ingeniousity to try and make do as long as possible with no cash. This includes many fun activities like the dine & dash, rob the homeless guy & my personal fav, how many drinks ordered by other people can you consume before getting caught.

heavydrinker, what about travel on the train w/out a ticket and no $$ as far as you can before getting kicked off and sneaking into a hostel and sleeping in someone else bed they paid for?

 
1. hitckhike
2. most hostels have a couch in the common room (I’ve actually done this once, but the hostel was full)

 
same here.  I’ll actually stick a bill or two under my shoe sole just for emergencies. 
 
But you’re still out of luck if you get gassed on a train because they will steal your shoes too! 

[8D]
 
I bring about 40-50 dollars US with me for use in the Airport before and after flights. Other than that, you don’t have to worry; unless you’re traveling to like Bangladesh, there are ATM’s EVERYWHERE. Just make sure you don’t pick a shady looking one haha

www.ectopmall.com it’s very good

I usually carry about $200 in US twenties as an emergency stash.  They’re easy to exchange if you run into some type of emergency — if it’s an emergency, you’re not going to worry about the dollar or two you lose on a bad exchange rate.