For about two months before the departure date, I watched the FX market.
The hardest part, for me, is deciding when stop playing the FX market. Despite the wholesale exchange rate, most consumers will have a higher rate since the majority of financial institutions (banks, FX desks) charge a fee. However, your personal bank, if it has a foreign or international department, will almost always give you a better rate than a FX desk at an airport or other places.
The other issue is determining the amount of cash you want to have on you. For hotels and tickets, I prefer using a card. Many smaller merchants prefer cash, so if you hope to go off the beaten track, bring some cash.
A credit card is more secure to me (if lost/stolen, call the company and cancel it. Cash? Eh, not so much). My preference has always been either cash or credit card. Traveler's Checks are more secure, but to me, convenience weighs in higher (and always: constant vigilance and monitoring of my personal things).
Keep in mind: many of the hostels around the Tour du Mont Blanc do not accept Carte Blanche (a credit card) since there is little need to in the middle of a mountain pass. Save the credit card for larger cities such as Chamonix or Courmayeur.
Right now, I have estimated expenses at:
Tickets (Train/Plane to Barcelona): 150
Accommodations on Mont Blanc (8 days camping at ~15/night): 120
City accommodations (21 days in hostels for 15-20/day): 370
Food (30 days for ~5 breakfast, ~10 lunch, ~15 dinner): 900
Round up to ~1500 Euro per person. Exchange rate $1.22:1Euro
From the WSJ: