The Defiant

It is important that you be able to Heal in battle and return t battle as soon as possible after rezzing.
To that end you should save your initial start up heals from newbie island so that you can start clicking heals as soon as you rezz, and make sure you carry a low lvl as well as a high lvl heal of each type once those are depleted.  While in combat a battle heal pack is essential, it can make all the difference between winning a fight or ending up at reclaim, these should be the highest lvl you can use without a buff.

More will be added to this topic soon

I lost 2 fights before by accidentally using first aid stims on the enemy. There's no side restriction on first aid kits apparently, so make sure to target yourself before using them! First aid kits are also good to restore nanopoints. This is really important since there are perks that drain nanopoints, trader nanopoint drains and finally that stupid rod of neleb's that drains nano! :S

If you have maxed body development and lots of health, what's even better is the ability to restore those hitpoints! It's like an extension of your health and hp restoration is probably more important than just having lots of hp. If you're an enforcer you might want both hp and nanopoints at the same time.. and if so there's nifty little (expensive) things called "restoration kits" Check them out here: http://arcanum.aodevs.com/pharmacy_stimkits.html

There are odd level first aid kits sold by a vendor in downtown Stret West/Last Ditch and maybe some other places too.

Some other useful first aid items are free movement kits which are for breaking roots (requires lots computer literacy). There is also burst of speed stims which boost runspeed for a minute. Nightmare therapy pills can also help to break roots and snares while using barrow strength gives temporary immunity (15 seconds, 20 minute lock) to roots and snares and combined with runspeed kits are good for escaping.

On the subject of items, there's bunches of random ones out there that are useful and have all types of effects.. too many to list here, but it includes things like barrow strength's counterpart, withered flesh and his big brother, assault class tank armor. Many types of hacked grafts, reflection bracers and novelty devices that are available in shops, etcetera.

After I die, if I'm around a surgery clinic I go click on that to recover hp and nano, though, it's probably not cost efficient at all!

And don't forget to ob  ;)