Calculate the total mass of 6 empty containers, each weighing 495 g, correct to 1 decimal place.

Since $1 \text{ kg} = 1000 \text{ g}$,

$$\text{Total mass of empty containers} = \frac{2970}{1000} \text{ kg} = 2.970 \text{ kg}$$

$$2.970 \text{ kg} \approx 3.0 \text{ kg}$$

The total mass of the 6 empty containers, correct to 1 decimal place, is $\boxed{\text{3.0 kg}}$.