LOL! Nobody pays the OP any attention and keep talking about the Psycho Mantis fight.
Anyway, if memory serves, there's an option to set the L2/R2 buttons to quickly choose the last item you had and there's an option to make Snake go from having an item equipped to having nothing equipped. Either way, the best way to choose weapons and items is to hold down the button (can't remember if it's L1/R1 or L2/R2 and I'm too lazy to fire the game up and check right now), and highlight the thing you want to use.
If you walk in front of a door and it opens, you have access to that level. If it's still locked, you'll get a higher card later on. Cigarettes can be selected and you'll know you're using them because Snake's health will slowly go down.
Any time you're in doubt about where to go (and I mean ANYTIME) press the select button and ask one of your partners for help. The game tells you everything you'll ever need to know about where to go if you know who to ask. It seems boring this day and age but at the time, listening to people talk on the codec was amazing. Also, much of the story takes place during those conversations. Don't EVER skip them. You'll never get lost.
Also, you may need to contact Meryl on the codec. If that's the case, her "phone number" is on the back of the MGS box. If you don't have the box, it's 140.15 .
