You don't need a secondary when starting. Good pistols/smgs are expensive and will most likely cost you more than a good starter AEG. You'd be much better off spending that money on buying a better and reliable primary and maybe a good radio. Don't forget to stock up on mags, more and more games have ammo restrictions, so you might as well start with a box of 8-10 low capacity or real capacity mags.

^+1

2/10 times I wish I had a pistol in CQB scenario.

If you play outdoor, you'll most likely never use a secondary if you running a decent AEG in my opinion.

Some people "SWEAR" by their secondary, but again, my opinion .

Pistol shooting is the most difficult skill to acquire and maintain.

The skills you acquire with a pistol will transfer to a rifle.

If you carry a pistol make sure you use it every game. It'll pay off in the long run.

Quality aeg. Armalite platforms are popular.
Cheap sling
Magazines if you dont want a tactical maraca (hicap) but if you get age verified you can buy a gun package.
Quality eye protection. Every field is a bit different so make sure you adhere to local rules.
Quality boots with ankle protection. Nobody likes a rolled ankle. I have seen people show up in sneakers and get told off.
If you want mouth protection to prevent get a tooth hit (rare but it happens)
A package of quality bb's
Battery/charger unless you get a gun with one. Drop the extra cash on a decent smart charger.

Thats a out it. If you wear cargo pants you can carry 3-5 mags without needing a vest. You can get better camo, a vest and accesories later on.

Best advice I can give besides what everyone else says (spend the extra on good eyepro and a good gun, and try someone else's before you buy to know you like it and it fits with your body/play style) is thus;

Do NOT skimp on footwear. You're on your feet all day, walking and running and climbing. Your feet are going to get wet. You're going to trip and slip and fall. Get good boots that are waterproof and give good ankle support.

depending on the play style and how seriously you guys play, a decent basic package (in my opinion for someone getting into the sport at least) is a g&g raider (comes with one high cap mag) thats about 200$, a battery usually goes for anywhere from 10$-80$ depending on nimh/nicad/lipo and voltage and mah. A paintball mask will do the trick. they can be had for about 40$ and bbs about 20-30$. go to an army surplus store, pick up a set of bdu's or even some form of camo style clothing you may have already.
thats just the absolute minimum

or get av'd and get the whole package for about the cost of a normal retail cost of a gun alone

This

Seen too many a time kitted out head to ankle and running with white sneakers. Good boots should last you years.

Good Boots properly tied are as basically important as eye pro. Yes ankles will heal (errr heel? lolololololol) but nothing sucks more than busting your ass getting all your shit in order and then busting an ankle at the start of the day. It sucks driving back home. Sucks even more if you got driven there and now gotta sit around all day.