I am looking for birthday present ideas for a 19 year old son from his mother.
I would give him a gift certificate for his favorite store.
When my son was that age (ten years ago, a student and working part-time) the gifts he liked the most were gas station gift cards and fast-food gift certificates. If he has a "significant other" a restaurant gift certificate or a couple of movie tickets might be welcome, too.
I just ask my sons what they want, and then buy that. Another thing I like to do is take them shopping for clothes, and then I buy them what they like, and have the fun of choosing.
Other useful gifts are a shaving kit, leather gloves, and sports equipment things like ski goggles.
My youngest son wanted a winch for his truck for a grad gift and then a powerful battery for a truck to run the winch. This is not something I would have thought of on my own! One year I gave each of my sons a battery charger for Christmas. My middle son who likes to cook likes appliances like rice cookers. You should ask!
I am presuming this 19 yr old is out on his own. Mine were still at local college living at home at this age.
Anyway, bath towels (Walmart has the nicest, cheapest ones for $4 or less), BUT get them in the beige, soft brown colors. Guys throw all their things together when doing laundry and these won't discolor very fast.
You can also get a gas card for his usual spot of fill up, gift card at the pizza place, etc. Guys want to buy their own clothes, and socks are not one sized fits all anymore.
If he is into car tools, etc check his brand of use, get a gift card for that. My 3 sons would decide what TOY they wanted together---new wire welder, new compressor and the one which serves them all is the car data computer--engine analyzer. You download your model and makes the first $300 at the shop of your discovery!