I have often done all the things you are tasked to do as a working professional, so I do know quite a bit about it. Other than advising your friend to hire a really competent professional and then being at the shoot yourself to observe and learn for a possible second opportunity, there is very little you can do to help create consistently first class pictures for your friend, unless you spend about six months practicing first. As others have suggested, your request covers such a broad range of subject matter - interiors, people and/or people with food, and food itself - that giving you any specific advice is really either a "fool's errand" or a full-time job.
As to cameras and lenses, you already have whatever you need if you would be just as creative as you need to be. Hey, just look through that little viewfinder thingy in the back of the camera and observe. Does it look right? Then it is. Lighting is what you need most and need to, above all, learn.
Instead, in an effort to be helpful, I will give you the same advice which served me so well over 30 years ago when the very talented pro I occasionally assisted for gave it to me. Buy, or preferably rent, yourself some very cheap "hot lights" - two or three tungsten halogen powered focusing floods or broad lights (i.e., TotaLights or Mole or Arri true focusing floods or "nook" or broadlights) in the 500 watt range and a couple of small (200 watts) Fresnel lensed focusing spots (sometimes called "midgets" in the industry). You'll need some barndoors for the true floods and perhaps a snoot or two for the spots. For most non-quick-melting food subjects, these lights, plus some B&W foamcore, some c stands, arms with gripheads, a mini boom, clothespins, A-clamps and Mafer clamps and some gaffer tape, a sheet or two of diffusion plastic, maybe a few colored lighting gels, plus 5 or 6 sandbags, will be all you need to do such a job properly. Generally, use reflected (off foamcores or ceilings/walls) or diffused (through plastic sheeting) light for soft lighting effects, the harder direct lighting mostly with the small Fresnel's. Most inexperienced amateurs would wonder if my suggestion sounds so "old school" as to be stupid. Why hotlights when you can also do such a job with flash which seems so much more "modern" and high-tech? Well, there are lots of reasons:
1) The ambient lighting in most quality restaurants is primarily tungsten (for now - until the EPA succeeds in ruining even our nights out to dinner), so that you will have a near color-match balance between your photo lights and the ambient background lighting. Life is simpler this way.
2) You can see exactly what your picture will look like (except for contrast/DR issues) with your own eyes and very quickly adjust and change your lighting until it simply looks good; flash modeling lights are never as effective at previewing your actual pictures for many technical reasons. This concept is true for both the food and the restaurant interiors.
3) Flash (except for truly ridiculously expensive - and not quite as "accurate" - Fresnel-lensed flash units) and other economically feasible lighting sources, like controlled photo fluorescents, just can't duplicate the control and effectiveness of a simple, cheap 200 watt Mole midget Fresnel spot, which makes it possible to make your food go from OK to great looking when you learn how to use it with precision and subtlety.
4) If, when taking your people shots, you don't have enough "shutter speed" with your tungsten, you can add a little supplemental pop to the people with a simple tungsten gelled potable flash unit, which, along with today's higher ISO possibilities, makes this use quite effective.
5) Once you know how best to light things with your tungsten experience, you can later use that knowledge with the harder to use (for this subject matter) flash lighting that you see so often. Or maybe just stick with tungsten. Whatever suits you best.
Last, per what you said in your OP, you don't always need very great depth of field in your shots, especially in your food shots, as, for the past 15 years or so, very narrow depth of field has been the more usual approach, perhaps even originally created out of necessity, but nonetheless still the current norm. Think small. Think mainly out-of-focus.
I hope all this advice helps, but I still think you ought to have your friend hire an experienced and talented pro the first time.