Maybe he intended to take a snack (or had already thrown it in the bag) and therefore had already set it and his pole outside on the porch, getting ready to leave. He wouldn't take everything with him, especially not his clothes, he wasn't running away, so who would take a full backpack with them. He ducks back in to get the phone, and some random (evil



) passerby (or someone that knew his dad and knew that he would be there alone, due to dad's vehicle missing or having seen him drive past alone earlier in the day) grabs Dylan's stuff, throws it in his vehicle, knocks on the door, tells Dylan "Hey, man, somebody grabbed your pole and took off." Dylan steps outside, random passerby says, "Come on, we'll go after him." No struggle at the house, missing items explained, and Dylan gone.
That's the only theory I have that allows for him to still be alive on Monday morning, and it would take a lot of coincidence, like the cell phone battery being dead or there being no reception, Dylan having to go back into the house, and the random passerby passing by at just the right moment. I guess stranger things have happened.