How quick will i lose m/muscle?

ive been training properly for about 3 years and last 2 or 3 months ive really stepped it up and gained quite a bit of muscle growth. Im now in afghan and while im training hard (twice a day) when i can there can be periods of up to about 2 weeks where i cant train properly/at all due to me being here. As most people who train properly im paranoid bout losing muscle if i dont train for few days even tho i know its impossible to lose it that quick let alone a few weeks. when im unable to train here im normally on rations too so my diet is poor and consists of about 3000 calories of mainly carbs. Anyone know of anything i can do to retain muscle or ideally keep gaining whilst no where near weights or anything that can really be used as weights. Im aware of body resistance eg. push ups pull ups etc but ideally would like to keep gaining. Cheers