Can I buy storage products for my street motorcycle?

Storage or luggage that I can lock to my motorcycle so I can carry groceries and stuff like that? Also can I lock my helmet onto my bike so it doesn't get stole or messed with?

depends on the bike if its a crotch rocket get a magnet bag , check out JPCYCLES

Most bikes yes.

I think the vast majority of bikes come with a helmet lock (at least one) so you can secure your helmet or keep an additional with you. You should also be able to find mounting equipment for your bike so you can add things like hard saddle bags.

What kind of bike do you have?

The most versatile choice would be tanks bags (magnetic and straps), and throw-over saddle bags (can be removed easily. If you want to carry groceries, you need to get a decent pair of saddle bags and or a trunk.

Most of the time, such accessories can be had.

Google is the best search engine I can think of.

If you aren't able to get these accessories for your make/model, I would suggest getting a large backpack. I have seen more than one fellow riding a crotch rocket with a backpack on their back.

Whatever you do do not get a magnet bag unless you do not value your gas tank. There are tons of after market bags both soft and hard for your bike,

Go to www.Deniskirk.com and just google "Luggage of (your model) of bike.

Givi makes excellent hard bags and brackets to fit most bikes. The bags come off by just turning the key and pressing a button. They are waterproof and hold lots.
http://www.giviusa.com