Avoid enemies easily
By opening the Menu often out in the field, you will encounter enemies much less often. This is a bug in the game that was removed in future releases such as Mother 1+2.
Cheap/Free Hospital Visits
The doctor charges you half your money currently on you. Just deposit all your money to make him charge you very little to none.
Infinite Bottle Rockets
After getting Loid in your party, return to the Sweet's Factory where you got your first bottle rocket. Now the trash can disperses infinite bottle rockets.
Keep Eve in the Party
During the boss battle versus R7308XX you can use the Flea Bags repeatedly; this can get the boss's offense to a point where he cannot kill Eve. The battle will eventually end after 255 per a fail-safe script in the code, and gameplay will continue as if the fight had gone normally - with one exception, the highly powerful Eve will remain in your party. This is only doable on the Famicom release and its Virtual Console ports. Mother 1+2 on the GBA, plus the US prototype of this game and its Virtual Console analogue removed the glitch.
Unlimited Magic Herbs
While in Magiciant in the northern area you can find a red weed sitting in the middle of a bunch of green weeds. "Check" the red weed and you will recieve the Red Weed. Now bring the Red Weed to the Fountaain in the North West of Magiciant and "Use" the Red Weed. The Red Weed will change into a Magic Herb. Do this as many times as you like to recieve unlimited Magic Herbs.