Distance. At your current size, that will have to start becoming the number one factor in your decision-making process. No matter how desirable the contents of the beach bag, it's well out of your reach, over an unknown stretch of hostile territory. The purse though, that's in direct sight, and only a short climb to get to.
Of course, the woman could pick it up at any time, you think to yourself as you stride closer. But then, between two giants as you are, any moment one of them could stand up or roll over and crush you, so worrying about the actions of the gods is about as productive as trying to halt the tides.
You lay a hand on the skin of the woman's side, bringing it away sticky with the same tanning lotion coating your back. Not the most trusty climbing surface. Pressing both palms hard and high against the wall of goo-coated flesh, you pull, lifting yourself, getting those feet in place as well. With a little practice, you manage some upward motion; as long as you don't make movements too sudden, you can 'slide' through the lotion, allowing its powerful suction against your puny form to keep you steady against the surface.
It's slow going, no lie, but you're soon atop the stomach, where standing upright becomes a struggle against the power of the lotion. By this point you're pretty much coated in it, spitting gobs from your mouth. You're probably not going to burn up, though.
Despite being so much higher than you were before, your vantage doesn't give you a better look at the lay of the land. To the south, those mighty feet, still intimidating at a leg's distance. Opposite, hills obscure a face. Timing your steps with the rising motions of the breaths the giant is taking in, you move across her toward the strap of her purse.
What wonders could lie within? you ask yourself as you approach the strap. Surely enough supplies to allow for the outfitting of a modest initial camp!
As your hand makes contact with the strap to pull the rest of you up, you realise your mistake. There is a loud slurping noise as your feet pop free of the quicksand-like lotion, but once you are atop the strap, that same lotion becomes slippery against the material, and standing upright proves impossible.
It's not too late to cut your losses and get away before anything goes wrong, just climb down the woman and back to the sand. But you're so close! You could perhaps just scrape some of the lotion off yourself if you spent a little time, and then the purse could still be yours...
But why stop there! Why not climb toward those distant hills, and explore this new landscape while you can!