It is not common to pray for something that is already in your hands. However, a diligent child or servant of will give thanks to God and then go on to pray for grace so as not to misuse, abuse, waste or hoard the provision. For instance, if you want a drink of potable water, and you have some in a glass before you, you do not need to ask anybody for water to drink. If on the other hand the water is in the refrigerator and you cannot reach it for any reason, then you need to ask for help. That essentially is prayer. You pray for things you cannot do for yourself when you want to due to some constraints. The intensity of these constraints determines the amount of prayer required, and so on.