Feed

Other than fresh food, guinea pigs (cavies) need hay and pelleted feed.  You can buy hay at many discount stores and Farm & Fleet pet departments, but I’ve found better quality and more for the money on Amazon.com: since I have “Prime”, I don’t pay shipping, and the pigs really prefer the lighter, more leafy quality of this hay.  Just search for: “Small Pet Select 2nd Cutting Timothy Hay”.  My pigs hate that stiff, stalky hay — they are truly spoiled, lol!

For pellets, your pig needs a pelleted feed made especially for guinea pigs that contains vitamin C.  I feed Blue Seal brand that I buy at a local feed store, or it is also available on Amazon.  It’s perfectly ok to switch to another brand if it’s more easily accessible in your area, but please don’t feed one that has nuts and seeds and all that “stuff” added to it; it just is unnecessary “junk” in your pigs food and may make him/her fat or may be wasted altogether.  Just make sure you make any changes gradually, and that your pellets are made for guinea pigs (with vitamin C added).  A well-formulated pellet, hay, and fresh food is a FINE diet.  I would suggest (for economic’s sake) to buy a large bag of the pellets and dividing it into gallon-size freezer bags; store them in your freezer, and take them out as you need them — that way, you keep your food fresh and pest-free, and save money rather than buying those little bags at the pet store for $9 or $10.

We have a garden, and if you buy a pig from us, he/she is already used to mixed lettuces, swiss chard, bell peppers of all colors, tomatoes, and brussels sprouts; and I purchase cucumbers, cherry tomatoes, carrots, green beans and other greens in the off season or on sale at the grocery store.  

Bedding

Some pet owners are happy to do the fleece/laundering thing; I made a 2×5 C&C cage myself for a special pet pig and found I liked the system more than I thought I would, and wouldn’t  mind adding another!  Those of you who prefer to use wood shavings, I have found the best “deal” in a HUGE plastic-wrapped bale of shavings at Menard’s home improvement store for only $5.99.  

Vitamin C

To make sure your guinea pig (cavy) is getting enough vitamin C, it’s a good idea to add some to his/her water.  I buy vitamin C crystals from Amazon; I buy Thompson Vitamin C Powder 5000mg.  An 8oz bottle is only $7.75 as of this writing.  If you only have a pig or two, you may want to find a vitamin C that measures into your pig’s water bottle (my crystals measure 1/4 tsp. to a gallon of water).  You need to keep your “C water” fresh, not keep it for several days or it loses it’s effectiveness.  And on the subject of water, check your water bottles frequently — they can become clogged and stop working, and the pigs will stop eating if they don’t get water… and it can lead to a very sick pig.  This also where weighing your pig weekly on a food scale (I velcro a basket to the top) can be beneficial.
Update:  While adding vitamin C to the water is a fine method, with a multiple-pig household I found it caused too much build-up in the water bottles which led to a lot of bottle washing!  I DO wash the bottles with bleach and dish detergent on a regular basis, but if I can extend the time a little while longer — why not?  We use filtered water here, so there is nothing else to build up in the bottles.  So I found another method online that has been working so far: I use ChildLife Essentials Liquid Vitamin C and give each pig 2cc directly.  It is orange flavored, and they think it is a treat, eagerly coming to the cage front for it.  There are pros and cons to this method; the pro is I know each pig is getting a precise amount of vitamin C (the water method depends on how much each pig drinks), the con is, using the same syringe for each pig “may” transmit disease if any pig is ill.  I feel comfortable with this risk because my pigs are shown on a limited basis, and do not live in a barn but in our basement in a climate-controlled area (finished walls, heat & humidity added in winter and a/c in summer).