I have been looking at some multiclass feats from the players handbook and noticed that many of them allow you to gain a a class feature as an encounter power (Such as Warrior of the Wild, Sneak of Shadows, etc). Is there was a feat, item, or some other way of gaining that class feature properly and using it as if you belonged to that class?
Pretty much not. Though there are some significant exceptions.
Multiclassing in 4e is intentionally kept to 1/encounter type stuff. There are always-on things (skill training) that you can gain, but for the most part the benefits are 1/encounter.
That said, most things that are once/encounter provide 2 turns of benefits (last until the end of your next turn). For instance you get Sneak Attack from the Rogue's MC feat for two turns. You mark a creature for a whole round with one of the fighter MC feats. Generally feats and items will support a class features, but won't give your more uses of it.
There are several MC feats that do provide more lasting benefits. The ranger list for example:
And the Fighter MC:
Several classes have similar feats to the fighter that, for the cost of a feat after the MC will provide access to a full class feature.
The other option is to create a "Hybrid" character. These options are laid out in PHB3 and when subsequent books introduce new classes they provide instructions for how to create a hybrid version of those classes.
Typically Hybrid classes carry fuller version of class features than MC (they are always on), but restrict these abilities to being usable only with the powers from that class (for instance, the Avenger only gets to roll twice against it's Oath target when he uses an Avenger power).