Basic Diet -
    There's a great number of things that can be part or in some cases all of a "basic diet"; which things, and how much, are prone to personal opinion!  However, here's some common ones, and my personal opinion on them:

• Lab block - "The" complete diet, scientifically formulated to be a 100% nutritionally complete diet for rats and mice; awfully close for hamsters and gerbils, too.  Sold under many names (rat & mouse food, rodent pellets, etc. etc.) under different brands, it's basically the same concept; small pellets or blocks of 100% nutrition.  A fair number of people feed this exclusively; however, that makes for an awfully boring diet!  Moreover, rodents, like people, vary by individual in what, exactly, constitues an exact diet; some individuals require more of this or less of that.  A more varied diet is more likely to provide the right stuff for individuals.  Still, lab block should be the "basis" of a good diet, ideally making up 50-80% of the overall diet.
• Seed - Usually marketed as hamster seed or gerbil seed; basically a mix of different seeds, sometimes with other ingrediants.  Makes a good addition, although seeds tend to be high in fat - keep this in mind.  Avoid mixes with large amounts of sunflower seeds; these, especially, are high in fat.  Hamsters and gerbils should probably have  a higher percentage of seed in the diet than rats and mice, as they're more "vegetarian" in diet.  Hyper-active gerbils can usually stand the higher-sunflower seed, higher-fat mixtures, though of course if they seem to be getting overweight, this no longer stands true.
• Dog food - Some unscrupulus breeders, nearly always breeders that breed rodents as feeders, use dog food as a complete diet; one need only look at the differences in dietary needs of dogs (carnivores) and rodents (omnivores, leaning towards the herbivore side) to realize that this should not be!  It does, however, make a good occasional addition to the diet, especially for rats and mice that could use a little extra protien in the diet (growing pups for instance).  Actually, I use dog biscuits instead of dog food, as these can be more easily bought in small amounts (if I only need a couple, for instance); plus I feel they have more fun with the larger-sized pieces!
• "Table scraps" - AKA "people food" :-)  Tends to make a very good addition to the diet, although of course it very much depends on what types of people food you're talking about!  Fruits and vegetables are good, as is pasta, breads and the sort, and smaller amounts of meat.  Basically, anything good for you is good for your rodent; that of course means no junk food!  Avoid chocolate especially; although it's probably not as deadly to rodents as it is to dogs, it's not exactly something you want to test!  Adult rodents also have varying tolerances for lactose, which is in all dairy products.  This can cause diarrhea in large amounts, but given in only small amounts most rodents have no problems with it.  It can be given to nursing mothers and young pups, of course, and again is a good source of protien and other good stuff for growing babies!
• Anything else?  Be imaginative!  Personally, I often end up feeding my guys parrot pellets!
• Overall diet?  I would say around 50-80% lab block, perhaps a bit less for hamster and gerbils.  Seed comes next.  The rest - people food, dog food, any other treats you wish to provide - come in last when it comes to individual amounts, but do provide a valuable addition to the diet, being the most "varied" part of it!

Feeding Equipment -

• Food dishes - Don't bother with these for gerbils.  They will just kick the food out, or knock the bowl over (I don't care how sturdy it is), or bury it.  For the rest of the critters, a sturdy food bowl is a good idea; it may seem pointless when all they do is cache the food in some hidden corner anyway, but it does help to tell how much they're eating.  Make sure it's unchewable and can't be (easily) tipped over; large, heavy crock-type dishes for dogs or cats work for me.
• Water bottles - Water should be provided in bottles as opposed to dishes; if you think your rodents are hard on the food dish, try them with the water!  The water's generally dirty in five minutes; the dish is knocked over or completely fileld with shavings within an hour or so ;-)  Water bottles are much easier to use, much cleaner, and all around better.  They do come with a couple warnings; first, *check* the bottle every time to clean/change it to make sure the water is flowing smoothly; sometimes a bit of bedding will get stuck in the tube, or the little ball will stick up in the tube; either may make it impossible for your pets to drink, which could quickly cause death.  The next warning; while water bottles don't *require* cleaning/changing everyday, it's very easy to fall into the trap of not doing so - don't.  Bacteria grow quickly in water like that, and you wouldn't want your pets sick!