The nice thing about having a smaller, compact physique is that you don't need a lot of drugs to maintain it. Thats a very competitive market you are in. "Fitness" is a very popular trend no days. So yea, I understand you always need to be ready for an oppertinity that comes around. Still, you can't always be on cycle, just waiting for the phone to ring. If you stay in good shape and you do have above average genetics for the fitness model look, it shouldn't take a ton of changes to dial in, with a little notice. As long as your body fat is low, the main concern I would have for a last minute shoot or appearance, would be your water manipulation. Manipulating sodium, water loading/restriction, and possibly using a low dose of a "safer" diuretic like dyazide should bring you in looking very tight. If you have more time, say 3 to 4 wks to get ready, fast acting DHT's like anavar or winstrol will help give you more of a grainy and vascular look. So a wise move may be to have some of this on hand so that you are ready to start at a moments notice. In a situation like the one you are coming up on, given more time than a month, possibly 2, you have more room to get ready. A low dose of prop along with somyoure Masteron P and even a little Tren A would take you as far as you could possibly want to go. Just be warned, too much of the hardening compounds may give you a drugged look, which comes across as unhealthy. For this reason, I'd keep the harsher drugs like tren, at lower doses.
Another direction to go may be growth hormone. It keeps you fuller, yet leaner and brings a glow to your skin and hair. 2-4iu of a higher quality GH will produce some nice long term gains without as much of the side effects you'd deal with on AAS, not to mention, you can continue using it during the periods you are off cycle.