Easy aerial and rigging wires.

Aerial wires, and for biplanes in particular, rigging wires, finish a model aircraft.
There are several tried and tested ways of doing this:

Stretch Lycra
My favourite! A bit on the thick side for 1/72 but so easy. This is the stuff that little old ladies incorporate into the cuffs of knitted jumpers to elasticate them. Cut it a tad under-length, secure one end with cyanoacrylate (CA) adhesive, stretch, and secure the other end with CA. You can cover several bays in one run. No drooping wires, and if you snag the the rigging, it has "give" and will survive. Can be bought from Aeroclub, as ART003, for a modest sum.

Stretched sprue.
Heat plastic sprue over a flame and pull to achieve the desired diameter. Cut to length. Difficult to achieve consistent results and some sprues don't cooperate, twisting in the process. Cutting to length is critical.

Wire.
Stretch to straighten then cut to length. The length critical and they are easily bent by handling.

Hair
Human hair is good for 1/72. Coarser horse hair will pass, just. With suitable drilling, and a long-haired donor, several bays can be covered in one run. Secure with cyanoacrylate (CA) adhesive.

Nylon monofilament.
Fishing line! Available in a range of diameters to suit the scale. Use with CA adhesive. Secure one end, pass through pre-drilled holes, tension and secure terminal end.

Photo-etch
Comes with the kit or available after-market and is OK with a bit of fiddling.