Definitely you are on the right track with the money as a symbol. Money represents everything McCandless is fighting AGAINST. His parents are wealthy and have everything they could need/want; Chris finds this unjust. Same with the trust fund. He felt he did nothing to earn it, yet had it all, while others went without.

In particular, the burning of the money is symbolic of McCandless's rejection of the way humankind revolves around money.

And yes, the wild is a symbol as well--it definitely represents freedom from the demands and restrictions of society. It also represents hopes, beliefs, dreams and the willpower to stay true to these things as well...