Animals provide more nutritional content per gram than plants. Don't get me wrong - I love animals! They're delicious! But seriously, if you are vegetarian and wish to survive, you may have to bite the bullet a bit. All the survival books in my collection have great pictures of different ways of trapping, spearing, bow-and-arrowing, thermonuclear-devicing, and so on, big game. Here's my take on it, based on what has worked for me.
As I was preparing this I realised there was way too much material for a single section, so I've subdivided it to make it more digestible (geddit?). I suggest you look at it in order - the simplest and more gross-sounding options are likely to be your best ones. Don't restrict yourself to sirloin.
Disclaimer. As you may have gathered I have done a bit of hunting in my time - strictly for food or wild animal (noxious pest) control ie. introduced animals that screw up non-adapted ecosystems. I'm not a trophy hunter. No offense to those who are, I just don't see the point. I have also based this web page as a whole on things I have tried and practised, so I know they work. That being said... I believe in being humane. Some methods I describe (eg. those based on hooking warm-blooded animals) are methods I have not used, but others have described and I know will work. While I would have no hesitation using them in a survival situation, I don't use them just for practice and the hell of it. So resist the hate mail - this is just what works and it could save a life. You will note also I generally advise starting small - grubs and insects, before going down the 'great-white-hunter' path. This is definitely not a macho exercise.
A basic hunting toolkit
I only carry a few things specific to animal trapping in my survival kit. Other items are just general things I carry.
Paracord. Hey, along with duct-tape, there is always a use for it. I always carry some Paracord 550 or similar. Use it for anything monofilament can't be used for.
Knife. Again, part of any standard kit. On long excursions I carry two. A folding sharp knife is used for the pointy-end of dealing with the animal and I use a slightly heavier one for any whittling of sticks and heavier cutting of bone.
Digging tool of some kind. Again, part of any standard kit - you should always bury your 'material that you had for dinner'. If you are not in the habit of carrying a trowel, a tin can from your garbage collection will do. Remember we carry all our garbage out.
Monofilament fishing line is specific to animal trapping and is invaluable for snares, entanglement, and (you guessed it) tying fishing hooks to. 20.5kg/45lb breaking strain is pretty good for all-round use.
Noose wire is also specific to animal trapping. Sometimes monofilament is not up to the task for snares, particularly for animals that can gnaw. There are a few places to get good wire. Wire trace from your local tackle store is good - but expensive. I carry a small roll of light stuff - 20 gauge/0.020"/0.51mm - for lagomorph-sized animals (rabbits, hares) and something bigger if in larger mammal and monitor lizard country. Cheaper options are picture hanging wire. Also good old electrical appliance wires can be stripped and used for snares.
Fishing hooks. An array of fishing hooks is light and easily enough carried, and obviously only used to collect animals. Don't get too carried away with matching them to fish species - small and sharp is the key for fishes, with larger sizes for other things. As you will see with catching fish and birds, they are for utilitarian expedient, not sporting, purposes.
Fishing swivels. A stash of barrel swivels are great for setting up (obviously) any fishing setups. They are also great for forming the loop on snares. And they look shiny and pretty.
That's it. Monofilament gillnet would be nice, and guaranteed to be useful if you have to catch fish and birds (and larger). I'm not in the habit of carrying it around. Slingshots, bows and arrows, rifles etc. are fun - but unless your objective is hunting, you are unlikely to just have them hiding in your pack.