It the simplest terms, when choosing gear loadout, it should meet all of the following specifications:
1. AMMO- Pouches which will easily fit the correct magazines for your particular gun.
2. WATER- Hydration is extremely important. You should always make provisions for carrying enough water.
3. COMFORT- Make sure your gear fits comfortably and you can easily move around in it before you have to use it.
4. DURABILITY- Make sure your gear will stand up to the* inevitable wear and tear of playing airsoft.
5. MISCELLANEOUS- Its always good to have a general use pouch for stuffing random items. Things like food, extra clothing, flashlight, compass, map, or even for carrying extra magazines or use as a dump pouch if need be. Keep in mind, the more adaptable your gear is to the needs of the mission, the more successful and comfortable you will be.
Now, when it comes to choosing a specific type of gear, you basically have to choices for load bearing systems.
Load bearing suspenders
http://www.tacticalmarkers.com/catal...DE-244x374.gifThis loadout would involve a pair of suspenders attached to a utility belt on which you would attach magazine pouches, cantines, a holster, a butt pack for extra gear as pictured above, and anything else you might need. A rig like this could be put together largely out of surplus gear and could be assembled relatively inexpensively. Magazine pouches designed to hold m-16 magazines, like those in the picture above, are easy to find and will generally accomodate many other types of similar sized or smaller magazines as well, such as those for the mp-5, g-3,FAMAS,etc. Additionally, load bearing suspenders almost always have loops at the shoulders for attaching extra pouches. A compass pouch may be attached here and is a good accessory to have. A load bearing suspender rig is good because its simple, easily customisable, and generally inexpensive and easy to put together.
Load Bearing Vest
http://www.totalpaintballgear.com/im...l-Tac-Vest.gifThis loadout involves a vest, like the one above on which magazine and other pouches are attached. Load bearing vests are subdivided into chest rigs, which have fixed pouches.
http://www.cheaperthandirt.com/VEST135-702-616.htmlAnd plate carriers, which are designed to carry body armor and usually have MOLLE webbing to allow for custom placement of pouches.
http://www.cheaperthandirt.com/MOLLE134-44930-1977.htmlAS with load bearing suspenders, a utility belt with a butt pack and pouches may be worn attached to or below the vest. A compass pouch can also be attached to the shoulder. With a vest with MOLLE webbing it is also necessart to purchase the necessary pouches to attach as will be practical. MOLLE style vests and pouches are widely popular because of their adaptabilty. The vest can be changed around to fit your needs, and the pouches can also be worn on a regular utility belt. The combination of a vest and a belt can offer the ability to carry more ammo and gear, but some people feel the added bulk can be undesireable at times. But, for the most part, a load bearing vest is widely preferred by many people. As with many things, the particular style and feel of gear is all a matter of preferance.
Additionally, you may wish to supplement either of these loadouts with any of several types of sub loads or leg rigs. This could be magazine pouches, a dump pouch, gasmask pouch, or pistol holster that hangs on the leg suspended from a belt.
http://www.optactical.com/stdrlegpo.htmlhttp://www.optactical.com/dumpbag.htmlhttp://www.optactical.com/mhotadrlegex.htmlAlso, you can buy a drop leg style rig that is only MOLLE webbing and you can customize your own leg rig with any type of MOLLE pouch.
http://www.optactical.com/stdrlegpl.htmlAlso, In addition to or possibly in place of a cantine, you may find that a hydration system like a Camelback is what you want.
http://us.st11.yimg.com/us.st.yimg.c..._1897_46479056The Advantages of a Camelback are that you simply drink from a tube that goes over your shoulder and you can carry a good ammount of water on your back. The few disadvantages are that they are somewhat difficult to clean and that they are not good for carrying water for purposes other than drinking like washing and cooking. They are also a great deal more expensive than a cantine.
And finally there are a few more odds and ends that you would do well to pick up for you loadout.
good knife and or multi-tool
flashlight
lensatic compass
small first aid kit
Remember, if you're new to buying gear, take some time to research and ask around. Buy a simple rig that can be easily customized and added on to as you play and learn more about what you want and what works best for you.