An electric toothbrush can indeed be quite nice...
If you need to feel something inside you, you could try a banana (you can peel it if you want, but use a firm one)... Just put it in a condom; a ribbed one is best.
Or try an eggplant with a couple of elastic bands put onto it at different places. As with the banana, put it in a condom. If you use it as a dildo, the edges of the rubber bands will stimulate your vagina.
If you are so horny that you 'need' to masturbate in a public place, you could try crossing your legs and squeezing your thighs together. This works best if you wear tight jeans; the friction of your inner thighs on the fabric will stimulate your clitoris... Try to move your leg up and down until the inseam of your jeans touches your clit, and then squeeze, and rub your legs together... Most of the time, that is enough to make me come.