"Sorry I don't know when I will need it next, you can get a good cheap one from XXX though"
"Sorry I use this/these a lot"
"No, sorry, I like to keep these things with me just so I know where they are / don't lose them"
"It's nothing personal, I just don't feel comfortable lending out my XX"
Alternatively like you said in a comment, if you don't need these things don't bring them into work, they can't borrow what isn't there. If you bring them in to work because you do need them then you can reply with "Sorry, but I need it".
The main point is to stay polite and respectful. But remember they are your things and you do have a right to say "No", just try not to be rude to your peers in the process!
Sometimes just saying "No, sorry" will work brilliantly, they can't formulate an argument against why youre saying no if you don't give a reason for it. This can be seen more as rude though, so be wary.
Some people will always think it's rude if you say no. No matter how you say it, there are lots of people who think they are entitled to everything they want when they want it, and they will take even the politest of no's as a personal attack.
For these people there is nothing you can say that won't be taken as rude. So sometimes you do just need to be firm and say no (still politely) and more importantly don't feel you have to give in to the pressure from these types of people.
Giving in might be the easiest option at the time just so they aren't angry, but then you will have the situation where people will wonder why he is the special case. Why do you lend your stuff to him but not to the rest of them etc.
So, stay firm, give a polite decline, and continue with your day, after all, you have a job to do.