Solitaire, in its many incarnations, is the ideal spontaneous game for one (and sometimes two, as in Double Solitaire), that is easily played with only a deck of cards and a flat surface.
Solitaire Without a Computer
Playing solitaire on the internet is a popular pastime but it is even better enjoyed at a dining room table, an outdoor picnic table or even the beach. (For these outdoor locales, when wind is a hazard, look for magnetic cards and boards available in game stores or line.)
Solitaire games are for all ages and all levels of difficulty and games can be modified to simplify for young children or challenge clever adults.