Some cheesy New Age cassette tape.
My friend and I went out before work, to try this "cool" game I had read about in Newsweek. We both laughed when we saw the tape, and wondered what was on it. I remember leaving a heart shaped wrist watch. Interestingly enough, someone emailed me months later asking about the watch. They had just visited the same cache, for their first time trip, and had taken the watch. They wanted to know if it just needed a battery, or it it was really dead (I didn't know, as it was an unclaimed lost and found item that had sat in a drawer at work for months).