Sometimes the gift shop even sells the basic strategy cards. Plastic, laminated, size of a credit card. Of course, the cards are generic - that is, not fine tuned for # of decks, count, rules, BJ odds (3:2 or 6:5, though I refuse to play @ 6:5).

The only time the house might object, IMO, is if the player is taking too much time each hand to look up the correct decision on the card.