This game is long, even with these gold and time saving clues.
Cheating
These techniques were not supposed to be used. They are available probably because the game programmers did not think about them.
Starting out
Try forming a party and transferring all food and weapons to one member. This is best done within the Castle, avoiding monsters with which you can't cope. Leave the town to save the game, quit out of the game and then relaunch it, delete the empty character shells, and create three more. The extra gold makes starting out a bit easier.
Avoid starting a game with four brand new characters whenever possible or learn to handle death. A starting team where all characters can cast "Sanctu"/"Heal" is a good alternative.
Gold from Death Gulch
You can accumulate gold pretty quickly from the Armory in Death Gulch. It's found on large island to the east of Sosaria, and is a treasure trove of wealth.
Use the [O]ther command to bribe guards to get out of your way. It can be learned in Moon (in Devil Guard in the NES port).
You can save a 100 GP bribe fee and a key by entering the maze south of the main entrance. Go north at the first place you can, then straight east as far as you can, and then north to inside the gate. Go east to the locked gate. This one requires using a key. Go south to the entry on the left side of the screen. Go west to the first north possibility, west to the next south possibility, and west again. This should put you next to a guard. Bribe him. To the west lies a treasure area, good for about 1100 gold (about 2000 if you have the Mark of Force).
It's good to have a Thief with high dexterity who can grab the chests, and a Cleric who can heal him. Repeat this process until you've got quite a load of gold, say 13000 or so. The "Appar Unem"/"Open" spell allows to avoid traps in the chest, but it can still alert the guards. If all of your players have the marks of Fire and Force you can clean up by stealing all the chests you find within it. If you have no powerful fighters, you may want to bring along a lot of powders to freeze time while you run outside to safety.
Boat bridges
Since most of your travels will be on land, you will have to leave any boats you may have acquired from time to time.
Be advised that ships are very hard to come by. Because of their relative scarcity, you don't want them parked anywhere in the open, because they will be destroyed if the whirlpool comes along. The best way to leave them and be assured that you will be able to find them later is to park them on the other side of the silver snake and exit via the moon gate. If you wish, you can even fill up this entire waterway with boats and eventually be able to walk right into the castle Death from entrance at the moon gate.
In the NES port you can only have one ship at a time. It seems like the whirlpool does still get them, but they don't seem quite as scarce.
Give blood and heal (NES)
In the NES port, the healers in some towns pay cash to whoever gives blood.
Make a party of four healers (Cleric, Druid, Illusionist, Paladin, Ranger). Give blood to the healer in Castle British or in Moon. Heal up while traveling back and forth between these two locations; fight some enemies on the way.
When a character gives blood, he/she suffers 100 damages in exchange for 30 GP. A party of level 5 characters (550 HP each) can earn up to 600 GP per visit.