i second the cargo pants. it goes well with slippers, sandals, runners (make sure you dont wear socks with slippers and sandals, lol), and almost any type of shirts/t-shirts will match. save the shorts for when you play sports or need to be light weight to move around. tucking your shirt into the cargo pants can be fine and you'll look proper. it can be a good change of looks once in awhile.
another idea is to get a fanny pack type bag and wear it like those single strap side sling backpack. you can find one that hold just your essentials when you go out like your cell phone, keys, wallet and of course your leatherman. the bag/pack can be also worn in the front to prevent ppl opening and stealing stuff from the back. also, if you need to be lightweight, taking off the bag is much quicker then to have to unclip everything off of your pants. example, toilets in china (literally, even restaurants, only have a hole in the ground) or a port a potty. you dont want anything to unclip and fall into the hole, EWW!!
i dont have much of a fashion sence myself, but i see how ppl dress and pick up on it. heck, i'm sure you'll probably notice alot of times that ppl may dress more of a geek or have a huge fashion clash then you do. as long as you feel comfortable in what you wear and carry, thats pretty much all that counts.