The boxes must not be filled to capacity and made too heavy. They are both difficult to get picked up by the movers and they are liable to open and empty their contents all over the place. Moving crews can handle heavy things. But you are not. And if the time comes to move a box from one place to another after the crews have left you will find it rather difficult.
If you have a few days available before the moving date and you are moving within the same area, it is advisable to move some of your things to your new address beforehand. Especially for things and equipment that you may need up and running in your new household immediately.
One more tip on this is to make sure that the volume and the weight of your belongings is distributed evenly and arranged according to the room they will be placed. It is strongly inadvisable to pack for example shoes in the same box as the kitchen utensils.
Packing during the last day is always questionable. Being in a hurry includes the danger of making mistakes and causing damage without reason. It is strongly recommended to pack things that are not of immediate or everyday use as early as possible along with additional TV sets, radios and computer peripherals. Packing will be a lot more careful and a lot more considerate. It will also require less packing supplies.
Keep everything that is of significant valuable with you at all times. Put them in your car or take them to the house of a relative or a friend that you trust implicitly to pick them up after you have moved. Remember to check your insurance policy for its provisions in reference to moving to a new house. Keep all the paperwork handy at all times.