This is a 20amp outlet, but before you go drawing 16amps/80% of that, you should verify that there is a 20amp breaker/fuse on the other end as well as 12 gauge wiring (thicker than the standard 14 gauge you find on most 15amp circuits). If there is only a 15amp breaker, then the max you can draw from that outlet is 12amp (80% of 15amps).

You mentioned your one device pulls 8amps - that leaves at minimum, 4 amps available for your freezer - what is the current draw of that device? If its 4 or under and the breaker is 15amps then you are OK. If it is over 4 then you have to ensure you have a 20amp breaker in which case the max you'd want to pull is about 16amps combined.

If it is a 20amp breaker, then you will need to find a power bar that is rated for 20amp - I think most of the time they are rated for 15 but if you look hard enough you will probably find one for 20. You could also replace that one outlet with a 2 recepticle outlet which would eliminate the need for a power bar.

The below steps describe how to disable a safety feature by removing GFCI protection from your circuit. Check with local codes and verify that the problem isn't simply a bad GFCI or malfunctioning appliance before considering following these steps.

It sounds like your normal outlet is wired to the GFCI, making it a protected outlet.

Turn the power off, and remove the GFCI. You should see Black and White wires connected to the "LINE" Terminals, and another pair Connected to the "LOAD" Terminals. Devices with motors can trip GFCI outlets due to inductive loads at start up or shutdown.

Get yourself some spare wire. If you don't have any, buy a foot of 14/2 household wire from the local Orange or Blue Big Box Store. Also pick up some wire nuts rated for 3 14 ga wires.

You'll need to cut 4-6 inch white and black "jumper" wires and strip the ends.

Disconnect all wires from the GFCI, and screw in the LOAD screws all the way. I like to tape them off with electrical tape.

Attach one end to the LINE Terminals, matching white to white and black to black. (Brass screw is black, Metal screw is white. Green screw is ground (green or bare).

Now wire the three white wires together with a wire nut. Similarly, wire the blacks. These are called Pigtails.

Wire the two remaining ground wires to the ground (green) screw on the GFCI.

Stuff the wires in and re-mount the outlet.

You've just unprotected the fridge and freezer. However, I'd put a label on the unprotected box "NOT GFCI" so that a future owner doesn't make any assumptions.

EDIT: There may be a code requirement to have all garage circuits GFCI protected. Check with your local authority before doing this.

NEC 2008

210.8 Ground-Fault Circuit-Interrupter Protection for Personnel.
(A) Dwelling Units. All 125-volt, single-phase, 15- and 20-ampere receptacles installed in the locations specified in (1) through (8) shall have ground-fault circuit-interrupter protection for personnel.

(2) Garages, and also accessory buildings that have a floor located at or below grade level not intended as habitable rooms and limited to storage areas, work areas, and areas of similar use.