Whoa! Those are a lot of questions, Imiezal! I'll do my best to answer them though...
Mushrooms
 Spoiler
-Mushrooms are found on grass-like parts all over Era
*Mushrooms sells for 5 gralats each
*Revive recommended
*Does a great combination with trash

Mining
 Spoiler
*Best done at Chinatown Mines

Mail
 Spoiler
*18-30 gralats per mail
*Revive recommended

Pizza
 Spoiler
*5-? gralats per pizza

Trade
 Spoiler
This is not a job

Trash
 Spoiler
*Tires= 6 gralats; Paper= 4 gralats; Newspaper= 4 gralats; Broken Bottle: 5 gralats
*Remove recommend
*Great combination with mushrooms

Car Missions
 Spoiler
*30-70 gralats per mission
*Dangerous (30% fail rate)

Gralat Pack
 Spoiler
*Fastest and easiest way to get gralats
*Recommended
**DO NOT BUY GRALATS IF YOU ARE LAGGING, WAIT UNTIL LAG GOES AWAY BEFORE BUYING GRALATS