The probability is high, that you will never fulfill such a commitment. Instead, set a goal of once a week. When you go, make it a very casual, strain and stress free event. In doing so, you will be more likely to go and maintain such a schedule. A little exercise is better than no exercise.
Gift certificates are the way to go.
Stocks, over time, have the highest rate of return over any investment. But don't buy individual stocks. Too much risk and too much research effort. Instead, select a good mutual fund where the fund manager does all the work. In fact, a good fund to consider in the Vanguard 500 Index Fund.