I love travelling (and I'm an international flight attendant), so I should be able to give you a few tips!
1. Sometimes Happy Cow doesn't have all the options in the place you're travelling to. Wherever you're going, Google (for example) "Budapest vegan" or "Budapest vegetarian friendly" and you should yield some good results! What cities are you going to? I've been all around Europe, so I could give some specific recommendations of places to eat.
2. Write down "I'm vegan" or "I don't eat meat" in every language of the countries you're visiting. Many restaurants dont have English menus, so learn what vegetarian means in their language so you can identify what options you have at non veg restaurants. You can then ask for no eggs/dairy in their language (the main diets in many European countries focus heavily on meat, so they may not understand what vegan means). On that note, many of the countries I've visited (particularly in Eastern Europe) garnish their meals with meat. Even the seemingly vegetarian options came sprinkled with bacon bits!
3. There are always vegetarian options available (although in the smaller cities, they'll be harder to find). I've found that big, touristy cities generally have a few vegan/veg friendly restaurants so you'll be fine there. However, smaller cities or cities not as frequently visited by a large number of tourists might only have a few omni restaurants that have vegetarian options, and definitely no vegan ones. In my experience, this was true in many places in Eastern Europe (and definitely in China/HK etc), where it was also much more difficult to communicate my dietary requirements due to the language barrier. You might find in some places you'll have to get your own fresh food from markets, or be OK with not being as strict.
4. Preorder a vegan meal prior to your flight. Always reconfirm directly with your airline (not your travel agent - usually they do not pass the information or order onto the airline) 48 hours before departure to ensure they have your request. Watch out for the 'vegan' margarine and milk on your plane food tray. From what I've seen, they're dairy/lactose free but not actually vegan.
