Storage of Mileage and Trip info into memory

Other Hardware Storage
2

If you only have one variable to store, you can simply store it at eeprom address 0.

To save

unsigned long odoMeter = 3456;
EEPROM.put(0, odoMeter);

To retrieve

unsigned long odoMeter;
EEPROM.get(0, odoMeter);

If you have multiple variables, it's a little more complicated. You can use something like

#define ODOMETER_ADDRESS 0
#define AVGFUEL_ADDRESS (MAXSPEED_ADDRESS + sizeof(unsigned long))
#define MAXSPEED_ADDRESS (ODEMETER_ADDRESS + sizeof(float))

The odometer data will be stored at address 0. The average fuel will be stored after that (it will be address 4 but is not really relevant). And the maximum speed will be stored after the average fuel.

The above assumes that the odoMeter variable is an 32 bit variable (e.g. unsigned long) and that the average fuel variable is a float (a float is also a 32 bit variable).