I would plant daikon, its a radish with 3 foot roots. It will help with the water, infiltration. fava beans are also good they are a good N Fixer, in the winter when most plants lose leave and they will also grow on the ground and suppress grass.
As for fruit/nut trees that you can grow here is a ist of a few.
http://www.tradewindsfruit.com/fruits_ornamentals_by_hardiness.htm
http://www.onegreenworld.com//index.php?cPath=1
Below Zone 8 (below 10F/below -12C)
Actinidia arguta Hardy Kiwi (to -25F)
Cydonia oblonga Quince
Salvia sclarea Clary Sage
Vitis californica California WIld Grape
Zone 8a (10 to 15F/-12 to -9.5C)
Actinidia chinensis Golden Kiwi Fruit
Actinidia deliciosa Kiwi Fruit
Butia capitata Jelly Palm
Butia eriospatha Wooly Jelly Palm
Camellia pitardii Camellia
Eriobotrya japonica Loquat
Morus nigra Black Mulberry
Tecoma sambucifolia Waranway
Zone 8b (15 to 20F/-9.5 to -6.5C)
Arbutus unedo Strawberry Tree
Berberis nevinii Nevin's Baberry
Brahea armata Mexican Blue Palm
Drimys winteri Winter's Bark
Feijoa sellowiana Feijoa
Morus macroura Himalayan Mulberry
Myrtus communis Myrtle
Zone 9a (20 to 25F/-6.5 to -4C)
Acmena smithii Lilly Pilly
Aegle marmelos Bael Fruit
Araucaria bidwillii Bunya-Bunya, False Monkey Puzzle Tree
Azara petiolaris Holly Azara
Brahea edulis Guadalupe Palm
Canna edulis Achira, Arrowroot
Carica quercifolia Oak Leaved Papaya
Carissa macrocarpa Natal Plum
Caryota urens Wine Palm, Toddy Palm
Casimiroa edulis White Sapote
Casimiroa tetrameria Wooly-Leaved Sapote
Ceratonia siliqua Carob
Citrus sp. Citrus Fruits
Clausena lansium Wampee
Dovyalis caffra Kei
Apple
Eugenia aggregata Cherry of the Rio Grande
Eugenia uniflora Surinam Cherry
Fuchsia boliviana Bolivian Fuchsia
Fuchsia triphylla Honeysuckle Fuchsia
Macadamia integrifolia Smooth Shelled Macadamia Nut
Malpighia glabra Acerola
Myrciaria cauliflora Jaboticaba
Prunus lyonii Catalina Island Cherry
Vaccinium gaultheriifolium Chinese Blueberry