Reddit mentions of Langenscheidt's Pocket Dictionary Classical Greek (Langenscheidt's Pocket Dictionaries)

I'd recommend getting the Liddell-Scott Greek-English lexicon, which is the standard for most Ancient Greek. You could go for the intermediate size, which would have probably most of the vocab you'd need for something like Plato and Aristotle.

You could also go for the full-sized one, which is like the Ancient Greek equivalent of the Oxford English Dictionary. If there's a word in ancient greek, it's in there. Now, a full Size version of the most recent edition is about $200. BUT there are ways around that.

• It's available free online at the Perseus project, if you don't mind having to have a computer around.
  
  
• You can also get the 1968 edition, which shows up on Amazon fairly frequently. It's sometimes grouped for sale purposes as merely a different edition of the "abridged" lexicon -- but if you check the publication dates of the various editions, one will be 1968, which is the date of the previous edition of the full sized version.
  
  In fact, there appears to be a full-size version on Amazon for $25 right now. That's the same price and location I got mine, and it was a STEAL. That's less than you'd pay for one of the smaller lexicons.
  
  
  Now the biggest obstacle there is portability. It's a beastly huge thing. So what I'd recommend is taking the money you'd save and spending $5-10 on the Langenscheidt Pocket Classical Greek Dictionary, which will still have the majority of the vocab you'll need; at least enough to hold you over til you get home to the Beast.
  
  Also: as a mod there I'd be remiss if I didn't recommend that you stop by (and maybe subscribe to) the subreddit /r/AncientGreek.