An incorrect but sometimes common stereotype of the non-profit sector is a poorly-funded or maybe even ramshackle group of operations. Yes, you'll still find those traditional "soup kitchens" out there to this day, supported by local churches or an occasionalional donation drive, but there is a lot more to this sector than that. Charities can be regional or nation, which means that they need to market and promote themselves like any other big organization does. Bring on the promotional products!
Take a closer look at large charitable organizations like the Red Cross and you'll see something that represents a well-oiled machine like any for-profit business. Does this mean that they need to approach promotional products the same way any for profit business would? Sometimes. Context is always important in marketing; one route does not meet the needs for everyone equally, and this applies to a non-profit organization as much as it would for anything else.
Potentially the difference would have been the availability of funds to spend on marketing efforts. A business has things like profit (of course) that can be converted into money to spend on the more ethereal things like marketing and branding. Budgages at non-profits can end up very limited, especially because the reputation of a non-profit can be a huge factor in its success. Some non-profits see it as a priority to keep the amount of money they spend towards "administrative costs" as low as possible. Critical to their reputation, even. In the case of a charity, how likely are you to give if they seem to spend half of their fees on themselves?
That said, the similarities to a normal for-profit business do mean following some of the usual guidelines. If a non-profit is going to be at a trade show and intends to give away corporate gifts to drum up some awareness they're going to want to keep the giveaways small. No one is going to want to carry them around all day if they've been given cumbersome promotional products. Avoid the temptation to just toss money into purchasing any little trinket you can find, either. Giving out an easy to carry but completely useless promotional item is just going to be a waste of money. Money that may more difficult to come by in a non-profit environment!
It can be really important to avoid letting budgetary concerns scare a non-profit from being creative. In fact, less room to maneuver may mean mean letting those juices juices flow and use promotional items that are not entirely obvious or common! Charities can attract a youngger and creative group of employees or volunteers, so it is important to tap into that resource. Take advantage of the fact that many people do not look at non-profits as a business, which can mean more freedom. Picking a promotional item that might not be entirely professional could be a bigger benefit to a brand than a hindrance!
If you are in the promotional products industry, it is important to not write off the non-profit sector as a source of potential clients. They're out there and they need your help! If you are a non-profit, the promotional items out there could be a critical contribution to getting some awareness out there and some contributions rolling in.