Yes you can reach sankri by own but by two Wheeler is difficult cuz of the snow. Road is very slippery for two wheelers. I would recommend you to take bus from dehradun to sankri. Once after reaching sankri take a package. It is difficult to carry food, tent, sleeping bags while trekking cuz of the steep climbing. If you take a package they will provide you food and everything including your missed trekking equipments which you need most.