As you shoulder your rucksack for this summer's short walk in the Hindu Kush, or wherever, the perennial jostle for space means that books have to work very hard to earn their passage, or they end up losing out to the Primus. The secret is to take one huge one or lots of little volumes.
The biblical proportions of The Seven Pillars of Wisdom lasted a four-month-long expedition to Central America and I still haven't finished it, much less understood the intricacies of Middle Eastern politics.
But who cares, TE Lawrence makes such a joyous adventuring companion.
In the small-is-beautiful category, Rose Macaulay's The Towers of Trebizond (Flamingo Pounds 5.99) fits snugly into the folds of a sleeping bag. She is a captivating traveller, with a charming mix of Joyce-Grenfellish eccentricity ("Take my camel, dear"), coupled with an elegiac affection for a world unblighted by package tours. She knew it couldn't last and it hasn't.
Martha Gellhorn's Travels with Myself and Another stiffens the resolve of anyone faced with the choice of another week in the rainforest, or one night of hot showers and room service in a Holiday Inn. Roll out that Karrimat right now, and wonder how on earth anyone managed to get themselves despatched to such inhospitable places.
If there's one book, though, to make you head straight for the Costa del Sol, it's Touching the Void, by Joe Simpson. Simpson's heart-stopping account of a South American climb that went terrifyingly wrong should ensure you never again tackle anything steeper than the escalator to the departures lounge at Heathrow.
Janette Wolf is the resources and media editor of The TES