From the very funny Ask the Past:
"[A traveler] should carry with him two bags: one very full of patience, the other containing two hundred Venetian ducats, or at least one hundred and fifty... furthermore, he should provision himself with good Lombard cheese, sausages, tongue, and other cured meats of every sort; white biscuits, some cakes of sugar, and various confections, but not a great quantity because they spoil quickly. Above all he should take plenty of fruit syrup, because that is what keeps a man alive in extreme heat; and also ginger syrup to settle his stomach if it is upset by too much vomiting."
Santo Brasca, Viaggio in Terrasanta (1480)
Airport security may take your fruit syrups, and customs may confiscate your cured meats, but no one can take away your suitcase full of patience.
Patience. I always forget to pack the damn patience. And the tongue.