In case you are not aware, Monday-Wednesday many universities hold these sessions with free food and drinks, and the faculty (including those on the search committee) typically stay in their room, while everyone else is floating around from one to the other. While this is a joy-full experience to the hungry students and to the hand-shaking professors, but for you this may be critical to getting your foot in the door. The experience and the atmosphere will be similar to approaching strangers in a bar. I know that this is hard to do, especially for introverts (which most of engineers and scientists probably are), but you need to be able to do it at this critical time in your career. So do whatever gets you comfortable. Practice before the conference. Read strategies online and watch videos with tips for striking up conversations with strangers.
Try to hit as many of these receptions as you can, starting with the hiring universities, obviously. When you enter the room, do your best to identify the important people (ie, the ones on the hiring committee). These tend to be the older folks, and typically, they will have a crowd of desperate job-seekers, such as yourself around them. You can also ask someone who is from that university if they can tell you who is on the hiring committee. Go and approach these professors. Note, that it is a good idea to arrive before the reception even starts, or at the very beginning, because the professors are more available at that time.
Usually, I started with extending my hand, introducing myself and then just starting to pouring about my grants, publications and research into their ears. Think of it as an "elevator-pitch", where you have just 5 mins to impress an investor (because, eventually, someone else will interrupt and steal your spotlight). Make sure that your name-tag is visible, and have your resume on hand, plus some business cards. Ask them for their card, and find out who else from their department is around that you could talk to. Maybe even ask if they would hand you off to the next professor.
For conversation topics and questions you should be asking, see my post about the interview:
Unless, you were approached a department representative at the poster session, this is a low yield activity, but you have to try anyways... if you were indeed approached and invited, then treat this as an effective mini-interview. Try to talk to EVERYONE from the department. Invite them to your oral talks, if you have any. You can even print those on the back of your card that you would be handing them.
Also, some schools will flat out offer to interview you at the conference (some of the more money-tight departments did that to me). Obviously agree to do that, go meet them up for coffee or whatever and have a chat. Not as good as an on-site interview, but better than nothing. And make sure to be prepared to answer the same questions as you would be asked at a real interview!
Also, also, make sure to invite people to your talks, both when you meet them and when you submit your packet to them online BEFORE the conference. You can indicate the date and time of your talks in the cover letter, and if they are interested, they may come... And also FOLLOW UP with the people that you've spoken to, after the conference, in order to indicate your enthusiasm for the position.
Finally, if you see me anywhere, feel free to ask me to introduce you to whomever is your target... I'll do my best to try, lol.