I have quickly learned that preparing your travel itinerary ahead of time can save you a lot of unnecessary stress and money on Advil for those sure-to-happen headaches. Finding and booking a place to stay is one of the things I make sure to do ahead of time when going on a shorter trip.
Depending on the time of your visit to the Gili Islands, I would highly recommend booking ahead of time during their high season. We figured that most accommodation would be sold out, however, we were surprised to have multiple locals approach us when getting off the boat asking if we needed a room. We didn’t look into details regarding the price, area, or set-up since we already had something booked. However, I suppose it is good to know that you can head over there without any real plan (though doing this during high season would not be the wisest decision, unless you enjoy sleeping on the beach).