When at all possible, make it yourself. Why? Simple economics: Someone has to prepare it. You can pay for the labor of someone else or you can do it yourself. Paying $4 for a small portion of watermelon that is cut up, or paying $4.50 for the whole watermelon, cutting it yourself, and having three to four times more food: that's the choice. The later gives you the same result for $1.25 to $1.50 per portion instead of $4.
The same can be said for prepackaged foods in the freezer or refrigerator. Does it take more time? Yes, but it can mean significant savings that you can spend elsewhere and it can mean more family time and cooking lessons for the kids that may create better eating and financial habits that may last a lifetime.
However, the big gains are in your health. Many prepackaged foods are full of huge amounts of sodium which your doctor will tell you is bad for you. It is a big reason why Americans consume two to three times more sodium than they should and why we have many health problems.
Whenever possible, avoid the pre-packaged foods. It will save you money, give you some fun, and improve your overall health.