What to do?

Personally, I have always dreamt of my man secretly booking me a day off from work. I wake up, get up and just as I'm about to start getting ready....... then we just hang-out for the whole day being lazy. Then maybe you could do the picnic thing or take a leisurely boat ride?

Try to think of things she likes to do, and food she likes to eat, it'd be really sweet to make a few or her favorite dishes if you want to go with the picnic idea. And if age permits have a bottle of wine, it doesn't have to be extravagant to be sweet and thoughtful. Good luck :)

I have a blue fender, lol. I looked at your guitar picture. But here's a song to learn to play for starter's I known you can play this, I just do: Love song by Tesla. Play it for your girlfriend at some point, she'll like the song. Look the tabs up online. It's generally easy after the first part.

You can also make her something, shows effort. Like you can make her her birthday card instead of buy it, or the cake if you can cook. But buying sometimes looks nicer, it depends on how good you are at cooking and stuff. Breakfast in bed is sometimes cool, too.

And the art of the surprise in itself is something to work on. You want to be nonchalant kinda in a way so that your good at surprising. So let her sleep in and you get a jump on the day, make sure to get up a little early, and get yourself ready.

And you can look for something your girlfriend used to do and doesn't get to do anymore (like a hobby or something) and take her to do that. Maybe she used to go to amusement parks or roller skate or go to concerts or the beach (like you wrote, these are just ideas) and doesn't get to do that quite so often anymore.