Puzzle Books

Yes & Know/Show & Tell
American, mid -80s, and came wrapped in cellophane with a funny white pen with orange top. There were various puzzles, quizzes, mazes etc, and all you had to do to find out the answer was to write with the pen. The answer was magically revealed, invisible ink style. 

So you'd get 100 circles, and you had to find the correct route without hitting some bad circle (hit and miss really), or a quiz which unfortunately for kids in the rest of the world involved a good knowledge of American state capitals, that sort of thing.

Lee Publications brought its first "Magic Pen" books to the public in the mid-70s, and a generation of travel-hating kids bowed down in thanks. The games varied, but the mechanism remained the same. 

The most common game was multiple-choice trivia, with correct answers revealed by the stroke of a pen. Other popular games included Football, Baseball and Bowling (the pen reveals your hits, yardage, scores, etc.), Hangman, Fleet (a Battleship knock-off), matching games, a maze game with arrows indicating your possible moves, and the detective game Line Up. 

Nearly everything was designed for solo enjoyment (oo-er missus) but the trivia games had rules for multiple players as well. And if games weren't your style, then "Magic Pen Painting Books" provided pages of colouring fun to take your mind off your travels.

The cover was pretty liberal in its age ranges ("From 8-108! From 11-111!"), but it wasn't too far off the mark. The games were genuinely fun, and since the pen never lied, there was no way to cheat. 

Just don't leave the cap of your magic pen - there's nothing worse than a long family car trip with blank Yes & Know pages and a dried-out, useless Magic Pen.

Fighting Fantasy
Book 1 was something like The Warlock of Firetop Mountain, Book 2 was Citadel of Chaos, Book 3 was the Forest of Doom, Book 6 was Deathtrap Dungeon and so on (and on and on and on). 

Although these were popular, they were pretty random in terms of your progress - you just had to keep re-trying until you happened across the correct path.

Choose Your Own Adventure
Much shorter than the Fighting Fantasy series, but using the same principle. These books had white covers and horrible cutesy American characters (think The Famous Five, add extra sugar and schmaltz, stir liberally).