A Transistor LED Flasher
The perfectly easy method is to obtain a compact LED unit that flashes by itself which is the same as normal LED except for the required circuitry included in the unit an example is a solar led flasher powered by solar cells; otherwise a simple astable (oscillating) circuit you can build will do the job as described in http://wild-bohemian.com/electronics/flasher.html The circuit at the top is probably the easiest to use, you may use just a LED and in that case replace the other LED with a diode, resistor or a piece of wire, just don’t leave it out, otherwise the circuit is another thing entirely and would not work.
You can change the flash rate by changing the value of the capacitors or resistor but be careful how you change the value because there is a relationship between the resistor ratio for each transistor and the transistor β. You may need to check a transistor data sheet to confirm this.
Alternatively, you may use a 555 timer IC with few resistors and capacitors powered by a simple DC V supplies or a 6 V battery. Your ability to assemble electronic components, solder them together and testing using few workshop tools like soldering iron, solder, cutter, wires, switch and circuit board is essential.
You could adopt the unit in fancy device like the Halloween blinking eyes; emergency exit pointer, simple toy, traffic indicator and non critical timing application etc. with few modifications.