Blackberries can be collected in nature for free. Even though its nice to be able to be self sufficient and we like to grow everything on our own land, it is in many situations meaningless to grow berries and fruits you can collect elsewhere for free.
Blackberries however is very popular, so if we want to be sure to get any - before other people take them - we find we have to have it on our own land. Also, if you grow them yourself, you can choose a thorn free plant :-)
I collect berries every other day, since they are not all ripe at the same time. I put them on a plain surface and stick them in the freezer for half a day, before I store them in a freezing bag. That way they wont stick together and I can take out the exact amount I wish to use.
Since we just started out our self efficiency project, we didn't get that many berries this year - but next year I want to make blackberry marmalade - great for pancakes :-) And besides... Everything I'm able to store in glasses wont take up space in the freezer.