So I'm only level..13? I think at the moment and I'm having problems selecting items or strats appropriate for my level.

When I go on places to find guides for my champs, I find that a lot of them encourage DPS gear on tanks first. However, of course, since I don't have these hyperpowerful runes and maxed masteries, I feel like unless my team is dominating I'm not doing it right, ...I mean I end up with a Trinity Force on Nasus before he can take any significant damage.

Same with jungling. At level 13 I tried jungling to a guide with Noc.

"Wolves First"
-Done-
"Liches"
-Done-..Like 50HP left
"Golems"

Uhhhh... /health potion on the way, /engage, /run

I feel like I'm handicapped and if I select a particular role, I end up handicapping my team because I'm not filling it properly.

Obviously all champs play differently and have different builds, but are there particular items that are "universal" that I should focus on earlier (At this level) first for my particular roles?

The first thing you'll notice is that jungling before 30 with most characters is not only hard, but in most cases, actually impossible. Warwick is one of the few junglers before level 30 that you can expect to be successful. That being said, remember that the guides do give you guidance for level 30 runes/masteries...Before level 30, if you're trying to min/max your strategies, you need to figure out WHY they chose these runes/masteries/builds and see if they make sense with the opponents you CURRENTLY have.

Not every guide works for every situation and most guides are traps for people under level 30. Learn to itemize by picking items IN GAME that counter what your opponents are building. Last hit better so that your gold income is higher than your opponents. Learn when and how to take Dragon and Baron and your buffs. These things will help you FAR more than a rune mastery page when you can't finish it.

If runes/masteries are important to you, remember that EARLY GAME runes > LATE GAME runes...until you meet organized teams this will be true most of the time. So some MR or Armor early game will help. Some champions need Mana regen or health or even movement speed. For the most part though, get what you can, but your items will be MORE important overall.

+1 previous post.

Jungle is good, but most champs DO require the full page.
Damage items are usually more important for champs than defenses. Ideally you find out what opponents are doing well, and concentrate on defense against those champs.
Runepages are useful, but are usually only a 5-10% increase in effectiveness. Don't get overly stressed about not having them if you are playing a laning champ, since most of your opponents will have similar setups.