Unfortunately, there isn't really any way to avoid what alcohol does to your system once you've drank although you can hedge against its effects by drnking a lot of water.
The reason you feel weaker is probably due to water retention or lack thereof. If you'll notice, while you may look slighty smaller in the morning after a night of partying, you probably also look more defined and cut. You're simply dehydrated. I know this is the case with me...I always look leaner after the morning after but it's just lack of water in my system. Also, a lot of it's mental...you may feel like you've slacked on you diet so you feel like you should be weaker since you've engaged in "non-bodybuilding conducive activities," LOL!
I always make sure to eat some clean food before I go to bed and most importantly make sure you drink tons of water and take an extra multi-vitamin. I've also heard extra vitamin C helps.