When you find a higher level of vegetable than you have previously possessed, make sure that you ship at least one vegetable of that level rather than eating it. This is because the level of seeds you can purchase at the local shop depends on the level of seed you have shipped. You'll never be able to purchase more than a level 1 turnip seed, for instance, if you eat every turnip you find at a higher level. The same concept also holds true for seeds you unearth in fields.
At the end of the day you may be out of energy before you're ready to retire for the night. If that's the case, you can still do activities to earn gold without spending RP. Equip the sheers and find the wild Woolies in Piveria Forest. You can press B to sheer them, even though they're wild. Your only reward is a single small fleece, but you can keep sheering Woolies as long as you like for easy money (note that you can turn 3 small fleece items into a yarn ball, which is helpful when you need to obtain practice materials).