Kimberly, Coda, and Dais:
Through our experiences with our own Westies, with Westie Rescue, and with several special-needs fosters, we have grown to recognize that for a Westie to thrive, it needs high-quality products and non-allergenic foods!  Here are just a few of the products with which we have had first-hand success!
Commercial Foods
Natural Balance (Dick Van Patten's) Duck and Potato Non-Allergy formula -- soft canned food only.  This is an ideal option for Westies with food sensitivities, and it can help eliminate brown beards and paw-licking.
Precise's Lite formula for Less Active or Overweight Dogs -- canned only.  This simple, turkey-based soft food is an ideal alternative for Westies with sensitivities to chicken or lamb.  As a bonus, its lite calorie content can help maintain or lessen your Westie's weight.  We started this food as part of a diet program when our Westies bulged, and after 9 months, they lost a combined total of over 6 pounds!  Plus, their brown beards, paw-licking, and itches were eliminated.
honorable mention:
(Though we have not personally tried these foods,
some of our Westie friends have had success with them.)
Solid Gold -- dry kibble and canned foods.
Flint River Ranch -- dry kibble, sold on-line.
Merrick -- dry kibble and canned foods.
We don't feed treats!  Too many of them contain the wheat, corn, soy, and sugar ingredients that bother Westies.  Instead, our Westies love 1/4 cup fresh or thawed peas, fresh carrots, fresh or steamed green beans, and potatoes.
Finding the Right Food for your Westie
1.  Avoid these common allergy triggers:
        wheat, wheat flour, wheat gluten                     beet pulp
        corn, corn meal, corn gluten                             flax, flaxseed, or flaxseed oil
        soy                                                                   kelp
        beef or beef products                                       brewer's yeast
        chicken (for some Westies)                              "meal" ingredients
        alfalfa                                                                -ose ingredients
        lecithin                                                              by-products

                  **  Do not buy by brand name alone -- READ the ingredient lists!  **
A brown beard, brown paws, consistent licking, and/or
recurring skin rashes
or breakouts can all
be signs that your Westie has an allergy, and it may be a diet-related trigger!
2.  Consider one of these retailers, where you can research ingredients
     and/or purchase your chosen food:
     Pet  Depot (Greenspring Drive, Timonium, MD 21093)
     Pet Valu (various locations)
     Paws for Pets (Harford Road, Parkville, MD 21234)
     Shear Grace (Deepdene Road, Baltimore (Roland Park), MD)
3.  Gradually switch your Westie to its new food over a minimum 7-day 

     -   Start by giving 1/4 portion of the new food, and 3/4 portion of the
         food being discontinued.
     -   Feed this portion for as many meals as required until your Westie
         eliminates solid stools.
     -   Then increase the portion of the new food to 1/2, while giving 1/2
         portion of the food being discontinued.
     -   Feed this ratio until your Westie eliminates solid stools.
     -   Repeat the steps, gradually increasing the portion of the new food.
Flea and Tick Protection
Many rescues have flea allergies, so flea protection is essential!
Frontline Plus -- Though no product can prevent fleas or ticks from landing on your pet, Frontline Plus is our preferred product for preventing fleas and ticks from reproducing on the dog or from living on the dog for any duration of time. 
Dietary Supplements
Glyco-Flex II -- a glucosamine supplement for joint health.  Excellent at improving knee and hip strength.
Vetri-Disc -- a chondroitin supplement for back health.  Excellent at improving back and disc strength.
DermCaps ES -- a skin supplement.  Contains fatty acids that improve the quality of your Westie's skin and provide a boost to overall skin health.
Over-the-Counter Meds
(check with your vet for the proper dosage based on your Westie's weight)
Children's Kaopectate -- to relieve diarrhea, upset tummies
Children's Benadryl Allergy -- to relieve bee stings, other allergic reactions
Ascriptin -- Maalox-coated aspirin, for temporary relief of aches until your vet can see you.
Chlortrimeton -- For regular relief of seasonal allergies.